IV. Reading Comprehension (2×15=30)Directions: In this section, there are 3 passages and 15 questions. For each question or statement there are 4 choices marked A, B, C, and D. You should make the correct choice.Passage 1 Cold, one of the most common diseases confronted with the human race, is caused by more than 100 kinds of viruses (病毒). It causes such symptoms as nasal congestion (鼻塞), sore throat, and coughing. The common cold was formerly thought to result from exposure to cold weather, a belief probably traceable to the fact that people tend to crowds together indoors at this time, causing a more efficient transmission (传播) of virus from person to person. Chilling (受冻), also believed to cause a cold, may contribute to infection but some studies suggest that it is not of major importance. No cure is known for the common cold and no preventive drug has yet been found. In the early 1950s, some drugs were claimed to be effective in the prevention of colds. Most physicians believe, however, that such drugs cannot affect the progress of the true, virus-caused cold. The American chemist Linus Pauling proposed that large doses (剂量) of vitamin C can shorten the duration of a cold and release its symptoms, but several studies have failed to support his claim. Present-day methods of treating a cold are directed toward the relief of symptoms and the prevention of complications (并发症). Bed rest is commonly recommended to avoid complications. According to recent statistics, the common cold is the primary cause of absences in schools and industry. In the United States, where individuals have an estimated average of two and a half colds each year, the labor force loses more than 150 million workdays annually. Questions:1. In the past, people believed cold was caused by ______. A. various viruses B. exposure to cold weather C. gathering in a small houses D. sharp change of temperature

A. various viruses
B. exposure to cold weather
C. gathering in a small houses
D. sharp change of temperature