力对刚体的作用效果取决于()。
A、力的大小、方向和作用点;
B、力的大小、方向和作用线;
C、刚体的质量;
D、力的大小、方向和作用点,刚体的质量。
参考答案:A
When the American constitution ______into effect in 1789,it didn’t contain any words guaranteeing the basic rights of ordinary citizens.
A.went
B.had gone
C.has gone
D.was going
The professor’s research finally proved to be ______, though he had spent a lot of money on it.
A.priceless
B.valuable
C.worthless
D.worthwhile