题目

在接近收费口的道路上安装了若干条突起于路面且与行驶方向垂直的减速带，减速带间距为10m，当车辆经过着速带时会产生振动。若某汽车的因有频率为1.25Hz，则当该车以_________m/s的速度行驶在此减速区时颠簸得最厉害，我们把这种现象称为_________。 答案：12.5，共振，20、Normally a student must attend a certain number of courses in order to graduate, and each course which he attends gives him a credit which he may count towards a degree, In many American universities the total work for a degree consists of thirty-six courses,  each lasting for one semester. A typical course consists of three classes per week for fifteen weeks; a student will probably attend four or five courses during each term while attending a university. Normally a student may expect to take four years attending two semesters each year. Of course, they can work for the degree over a longer period. It is also possible for a student to move between one university and another during his degree course, though this is not in fact done as a regular practice.                 Every course that the student takes will be given a grade, which is recorded, and the record is available for the student to show to prospective (未来的)employers. All this imposes a constant pressure and strain of work on students. But in spite of this some students still spare their time to take part in the student affairs. Elections to positions in student organizations arouse much enthusiasm. The effective work of maintaining discipline is usually performed by students who advise the academic authorities. Any student who is thought to have broken the rules, for example, by cheating, has to appear before a student court. with the enormous numbers of students, the operation of the system does include a certain number of activities. A student who has held one of these positions of authority is much respected and it will be of benefit to him later in his career. 68. Normally a student would at least attend ______ classes each week. A. 36       B. 16       C. 30        D. 12 69. According to the first paragraph an American student is allowed ___. A. to live at home and drive to class B. to live in a different university C. to make a particular course in a different university. D. to get two degrees from two different universities. 70. American university students are usually under pressure of work because_______. A. their academic performance will affect their future careers. B. they are heavily involved in student affairs. C. they have to observe university discipline. D. they want to run for position of authority. 71. Some students are enthusiastic for position in student organization probably because____. A. they hate the constant pressure and stain of their study. B. they will then be able to stay longer in the university. C. such position help them get better jobs. D. such positions are usually well-paid.