当质点的运动轨迹未知时不能用自然形式的运动微分方程。
查看答案
物体一旦受到几个力的作用,它一定要沿着这几个力合力的方向运动。
A. 对
B. 错
Doctors strongly recommend that fathers____(be) present at their baby’s birth.
If you____(follow) my advice to prepare well ahead, you wouldn’t have failed the exam.
The city would look more beautiful if people____(throw) rubbish on the streets.