问题 选择题

下列有关制取干燥的氧气和二氧化碳的实验中错误的是

A.发生

B.干燥

C.验满

D.收集

答案

答案:C

A、由于氧气可以用过氧化氢和二氧化锰来制取,制取二氧化碳是碳酸钙和稀盐酸来制取,所以都可以用不需要加热的装置来制取.

B、氧气是中性的气体,二氧化碳是酸性的气体,且两者都不具有还原性,所以都可以用具有强氧化性的浓硫酸进行干燥.

C、气体的验满是确认是否收集满的,所以应该放在集气瓶的口部,而不是插入到集气瓶内部去.

D、氧气和二氧化碳都不和空气的主要成分反应,且密度比空气大,所以都可以用向上排空气法收集.

故选C.

解答题
阅读理解

Normally a student must attend a certain number of courses in order to graduate, and each course which he attends gives him a credit (学分) 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 (学期). A typical course consists of three classes per week for fifteen weeks; while attending a university a student will probably take four or five courses during each semester. Normally a student would expect to take four years attending two semesters each year. It is possible to spread the period of 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.

For every course that he follows, a student is given a grade, which is recorded, and the record is available for the student to show to prospective(预期的) employers. All this imposes a constant pressure and strain of work, but in spite of this some students still find time for great activity in student affairs. Elections to positions in student organizations arouse much enthusiasm (热情). The effective work of maintaining discipline is usually performed by students who advise the academic authorities (权威). Any student who is thought to have broken rules, for example, by cheating has to appear before a student court. With the enormous numbers of students, the operation of the system does involve a certain amount of activity. 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.

72. Normally a student would at least attend ______ classes per week.

A. 36      B. 12     C. 20       D.15

73. According to the first passage an American student is allowed ______.

A. to live in a different university

B. to take a particular course in a different university

C. to live at home and drive to classes

D. to get two degrees from two different universities

74. American 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 positions of authoring

75. Some students are enthusiastic for positions in student organizations probably because_____.

A. they hate the constant pressure and strain of their study

B. they will then be able to stay longer in the university

C. such positions help them get better jobs

D. such positions are usually well paid