Today is Sunday. It is a sunny day. Mike and Paul are going to have a picnic in the park. There are many green trees. Near the gate，there is a lake. Some ducks are swimming on the lake.

    Mike and Paul are going to have lunch at half past eleven. Then they are going to read some books under a big tree.

关于图中的两类滑轮甲和乙，下列说法正确的是(        )

C

    In the United States, headmasters and teachers discipline (惩罚) students in several ways. The teacher often writes to or calls the students' parents. Sometimes students have to stay at school for one hour. If a student behaves very badly, the headmaster can stop the student having classes. The student can't come to school for one, two or three days. Mr. Lazarus, the headmaster of a middle school in Ohio, did not like to do so. When he didn't let the students come to school, they were happy. “A three-day holiday!” they thought.

    One day, a boy was in Mr. Lazarus' office. The boy was not behaving well in class. Mr. Lazarus telephoned the boy's parents. “If you come to school with your son, I won't stop him having classes,＂he said. The boy's father came to school and went with his son to every class. Other students looked at the boy and his father. The boy was embarrassed. After that he behaved better. And, of course, other students behaved better, too.

    Now headmasters all over the USA are trying Mr. Lazarus's idea. They too, think that students behave better when parents come to school.

上臂处于如图所示时，相关肌肉的状态分别是（　　）