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When you choose a freezer, remember it’s probably going to be with you for a long time. No single style or size is best, so it’s important to know which freezer is right for your needs. First, decide if you want an upright or chest model. Uprights are more convenient. Their storage space is more accessible and they take up less floor area. However, chest models are more energy-efficient because less cold air escapes when they are open. If you’re buying an upright, you’ll have to choose between frostless or manual defrost. Chest freezers are always manual. Frostless freezers automatically defrost at preset intervals and remove the water. Manual models must be defrosted by hand every few months or whenever frost accumulates to about a quarter of an inch. To help your freezer reach a ripe old age, try to find a spot that’s cool, dry, and away from drafts. Drafts and heat will raise the freezer’s cabinet temperature and make it work harder to keep cool. That means wasted energy and a shortened compressor life. Dry air is important because high humidity can cause the freezer to rust outside and frost up inside. With proper care, a freezer can serve you for 15 years or more. Frostless models require less care than manual defrost freezers. The interior of a frostless unit should be washed periodically with warm water and baking soda or a mild soap, rinsed, and dried. To get the most from your freezer, check regularly to make sure it’s providing a true zero-degree temperature. Keep the freezer at least three-quarters full. The emptier it gets, the more energy is wasted. If more than three pounds of food per cubic foot of storage space is added every 24 hours, the resulting high or low temperatures can damage the food. According to the passage, choosing the best place for your freezer means______。
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Longitude and Latitude The meridians of longitude are imaginary great circles drawn from pole to pole around the earth. By international agreement, the meridian of longitude passing through Greenwich, England, is numbered zero. The earth is divided into 360 degrees, and the meridians are numbered east and west from Greenwich. There are 180 degrees of longitude east of Greenwich and 180 degrees in the westerly direction. New York has a longitude of 74 degrees west (74oW.) which means that it lies on the 74th meridian west of Greenwich. Since the sun appears to travel around the earth in 24 hours, it will move 360/24 or 15 degrees in one hour. This reasoning can be used by navigators to determine their longitude. Imagine that we have set sail from Greenwich, England, after having set a very accurate clock, or chronometer, to the local Greenwich time. As we travel westward toward New York, we notice that the sun is going "slower" than our chronometer. At the time that our timepiece reads 12 o’clock, the sun has not quite reached the zenith. As a matter of fact, when our clock reads noon, what it really means is that it’s noon in Greenwich, England. Our clock continues to tell us the time, not at our present location, but at Greenwich. Let us wait until the sun is directly overhead (noon at our location) and then read the time on our clock. Suppose it reads i o’clock. This means that there is one hours difference in time between our longitude and that of Greenwich. As we mentioned earlier, this corresponds to exactly 15 degrees of longitude, so our longitude must be 150 W. The world is divided into 24 time zones, and each zone corresponds to 15 degrees of longitude. New York is approximately 5 time zones west of Greenwich, so the time difference must be about 5 hours. By maintaining chronometers on Greenwich time, ships can determine their longitude on any sunny day by merely noting the difference in hours between Greenwich time and local sun time and multiplying this difference by 15 degrees. Of course, longitude gives only half of the information needed to determine our precise location. We must also know our latitude, which tells us how far we are north or south of the Equator. The Equator is the zero line for the measurement of latitude. Circles are drawn parallel to the Equator to indicate other values of latitude. There are 90 degrees of south latitude. In the Northern Hemisphere there is a star called Polaris almost directly over the North Pole. This makes it possible to determine the latitude of a given point by setting our sextant (六分仪) to measure the angle between Polaris；the North Star, and the horizon. Mathematicians tell us that this angle is equal to the latitude at the point in question. To get idea of our location, therefore, we need to know local time, Greenwich time, and the angle between Polaris and the horizon. In order to determine latitude, the navigator must know
What is NOT missing in Mary’s briefcase Why was Mary sure that the briefcase was hers in the end
Before the 1500’s, the western plains of North America were dominated by farmers. One group, the Mandans, (31) in the upper Missouri River country, primarily in present-day North Dakota. They had large villages of houses (32) close together. The (33) arrangement enabled the Mandans to protect themselves more easily (34) the attacks of others who might seek to (35) some of the food these highly capable farmers stored from one year to the next. The women had primary responsibility for the fields. They had to exercise (36) skill to produce the desired results, (37) their northern location meant fleeting growing seasons. Winter often lingered; autumn could (38) by severe frost. For good measure, during the spring and summer, drought, heat, hail, grasshoppers, and other (39) might await the wary grower. Under (40) conditions, Mandan women had to grow maize capable of weathering (41) They began (42) it appeared feasible to do so in the spring. Harvesting proceeded in (43) stages. In August the Mandans picked a small amount of the crop (44) it had matured fully. This green corn was boiled, dried, and shelled, with some of the maize (45) for immediate consumption and the reststored in (46) bags. Later in the fall, the people picked the rest of the corn. They saved the best of the harvest for seeds or for trade, (47) the remainder eaten right away or stored for later use in underground reserves. With appropriate (48) of the extra food, the Mandans protected themselves (49) the disaster of crop failure and accompanying (50) .
Migration is usually defined as "permanent or semipermanent change of residence". This broad definition, of course, would include a move across the street or across a city. Our concern is with movement between nations, not with internal migration within nations, although such movements often exceed international movements in volume. Today, the motives of people who move short distances are very similar to those of international migrants. Students of human migration speak of "push" and "pull" factors, which influence an individual’s decision to move from one place to another. Push factors are associated with the place of origin. A push factor can be as simple and mild a matter as difficulty in finding a suitable job, or as traumatic as war, or severe famine. Obviously, refugees who leave their homes with guns pointed at their heads are motivated almost entirely by push factors (although pull factors do influence their choice of destination). Pull factors are those associated with the place of destination. Most often these are economic, such as better job opportunities or the availability of good land to farm. The latter was an important factor in attracting settlers to the United States during the 19th century. In general, pull factors add up to an apparently better chance for a good life and material well-being than is offered by the place of origin. When there is a choice between several attractive potential destinations, the deciding factor might be a noneconomic consideration such as the presence of relatives, friends, or at least fellow countrymen already established in the new place who are willing to help the newcomers settle in. Considerations of this sort lead to the development of migration flow. Besides push and pull factors, there are what the sociologists call "intervening obstacles". Even if push and/or pull factors are very strong, they still may be outweighed by intervening obstacles, such as the distance of the move, the trouble and cost of moving, the difficulty of entering the new country, and the problems likely to be encountered on arrival. The decision to move is also influenced by "personal factors" of the potential migrant. The same push-pull factors and obstacles operate differently on different people, sometimes because they are at different stages of their lives, or just because of their varying abilities and personalities. The prospect of packing up everything and moving to a new and perhaps very strange environment may appear interesting and challenging to an unmarried young man and appallingly difficult to a slightly older man with a wife and small kids. Similarly, the need to learn a new language and customs may excite one person and frighten another. Regardless of why people move, migration of large numbers of people causes conflict. The United States and other Western countries have experienced adjustment problems with each new wave of immigrants. The newest arrivals are usually given the lowest-paid jobs and are resented by native people who may have to compete with them for those jobs. It has usually taken several decades for each group to be accepted into the mainstream of society in the host country. The author thinks that pull factors______
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