A. 正确 B. 错误
A. equally sharing the load B. jammed together C. as far apart as possible D. rove to the highest mechanical advantage
A. 聚乙烯(P B. 聚苯乙烯(PS) C. 聚氯乙烯(PV D. 纸
A. 1 B. 2 C. 3 D. 4