一个质点只要运动,就一定受力的作用,而且运动的方向就是它受力的方向。 ( )
Goods are carried by several of transport--on road or rail, by sea or air.
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
免费的网站请分享给朋友吧