杠杆是一种简单机械，能绕着一个固定点转动，具有（）的作用。
A、变化力值；
B、平衡重力；
C、重力臂。
参考答案：A
— I borrowed 10 dollars from Cathy, but she insisted that I had borrowed 15 dollars from her.
— I _____ you the money. Why didn't you ask me? [ ]
A. must lend
B. could have lent
C. would lend
D. should have lent
起动前的检查应做哪些检查？
