阅读理解 我有一个疑问一题对应的这段话 我摘出来了 是90年的四级真题Normally a student must a

阅读理解 我有一个疑问
一题对应的这段话 我摘出来了 是90年的四级真题
Normally a student must attend a certain number of courses in order to graduate, and each courses 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. While attending a university a student will probably attend 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 course, though this is not in fact done as a regular practice.
1. Normally a student would at least attend __________ classes each week.
A) 36 B) 20 C) 12 D) 15
答案是B 我觉得是C,求讲解!