一辆客车、一辆货车和一辆小轿车在同一条直线上朝同一方向行驶，在某一时刻，货车在中，客车在前，小轿车在后，且它们的距离相等。走了10分钟，小轿车追上了货车；又走了5分钟，小轿车追上了客车。问：再过多少分钟，货车将追上客车（）
A．10
B．15
C．20
D．30
参考答案：B
解析：
设小轿车速度为x，货车为y，客车为z，某一时刻的相等间距为S，可得[*]，可求出三车速度之间的关系为x=4y－3z，代入(2)式中可得出[*][*]，因此货车从开始到追上客车总共需要30分钟，则小轿车追上客车后，货车追上客车还需要30－15=15(分钟)。故本题正确答案为B。
| 阅读理解。根据短文内容，从下框的A-F选项中选出能概括每一段主题的最佳选项。选项中有一项 为多余项。 | |
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| Gift Giving 1.______ There are many occasions (场合) for giving gifts in modern industrialized societies: birthdays, naming ceremonies, weddings, anniversaries, New Year. It is common to give gifts on many of these celebrations in western cultures. In addition, special events, such as one's first day of school or graduation from university, often require gift giving. 2.______ What is happening when we give gifts? Most important, we are exchanging gifts. If someone gives me a gift for my birthday, I know that I am usually expected to give one on his or her next birthday. A gift builds up or confirms a social obligation (义务). 3.______ Gifts tighten personal relationships and provide a means of communication between loved ones. People say that a gift lets the recipient (接受者) know we are thinking of them, and that we want to make the person "feel special." We want people to feel wanted, to feel part of our social or family group. We give presents to say "I'm sorry." Sometimes it is difficult for us to find a present that someone will like. Sometimes we give things that we like or would feel comfortable with. In all these cases, the gifts are sending out messages-often very expressive ones. 4.______ People tend to talk about presents in a fairly loving way. A woman whose mother had died years ago described the many gifts around her house. These were gifts that her mother had given her over the years:"I appreciate these, and they mean something to me," the woman said, "because I remember the occasions they were given on, and that they were from my mother, and the relationship we've had." The gifts remain and keep the relationship alive in mind. This woman felt the same way about the gifts she gave to others. She hoped that the recipients would look at her gifts in years to come and remember her. 5.______ Emotions (情感) like these suggest that a positive spirit still lies behind gift giving. They prove that the anthropologist Claude Levi-Strauss was wrong to say that modern western gift giving is highly wasteful. Studies in Canada and elsewhere have also shown that this is not the case. Each gift is unique even if so many are given. The emotional benefit for those who exchange gifts is the very reason for the tradition to continue. |