题目内容

一个进程分配给4个页帧(下面的所有数字均为十进制数，每一项都是从0开始计数的)。最后一次把一页装入到一个页帧的时间、最后一次访问页帧中的页的时间、每个页帧中的虚页号以及每个页帧的访问位(R)和修改位(M)如下表所示(时间均为从进程开始到该事件之前的时钟值，而不是从事件发生到当前的时钟值)。虚页号页帧加载时间访问时间 R位 M位 2 1 0 3 0 1 2 3 60 130 26 20 161 160 162 163 0 0 1 1 1 0 0 1 当虚页4发生缺页时，使用下列存储器管理策略，哪一个页帧将用于置换解释每种情况的原因。改进的Clock算法。

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假设二叉树采用二叉链存储结构存储，设计一个算法，求出根结点到给定某结点之间的路径，要求：写出二叉树采用的存储结构代码。

假定硬盘传输数据以32位的字为单位，传输速率为1MB/s。CPU的时钟频率为50MHz。采用DMA控制器进行输入输出操作，假定DMA的启动操作需要1000个时钟周期，DMA完成时处理中断需要500个时钟周期。如果平均传输的数据长度为4KB(此处，1MB=1000KB)，问在硬盘工作的一次传输中，处理器将用多少时间比重进行输入输出操作，忽略DMA申请使用总线的影响。

孟德尔选取豌豆作为实验材料，因为它是一种性状的一年生植物。

A. 对
B. 错

Feed the World with Potatoes1 As food prices continue to rise rapidly, there is growing concern about the effect it will have among the world"s poor.2 Increasingly, experts are looking to the potato as a possible low-cost solution to feeding the hungry. To emphasize the issue, the United Nations has called the potato "a hidden treasure", and named 2008 the International Year of the Potato. Here"s how potatoes could end the food crisis.3 The potato matures more quickly, on less land and in harsher climates than most other major crops. Up to 85 percent of the plant is eatable, compared with around 50 percent of cereals. Its broad adaptability to a wide variety of farming systems is also noteworthy.4 Potatoes are an excellent source of complex carbohydrates ( 碳水化合物), which release their energy slowly, and have only 5 percent of wheat"s fat content. They contain only a quarter of the calories of bread and, according to the Potato Center, when boiled, potatoes have more protein and nearly twice the calcium (钙) as corn. Additionally, they are good sources of vitamin C, iron, potassium (钾) and zinc (锌).5 The Food and Agricultural Organization recently surveyed food price inflation in over 70 of the poor countries. Cereal price inflation was much higher and far more widespread than for potatoes. A significant factor behind the potato"s affordability is the fact that unlike other agricultural products, the potato is not yet a global commodity, and has therefore not attracted speculative investors. Raw potatoes are heavy and can rot during transit, so global trade has been slow to take off. Also, potatoes are susceptible (易受影响的) to infection with disease, hindering (阻碍) export. According to analysts" estimates, less than 5 percent of potatoes are traded internationally, with prices driven primarily by local tastes instead of international demand. Paragraph 2 ______ A. Higher Output B. Healthy Food C. Growing Importance of Potatoes D. Potatoes" Lower Inflation E. High Price F. Major Food Crops