质量为2 kg的物体，放在水平面上，受到水平拉力F=4 N的作用，由静止开始运动，经过1 s撤去F，又经过1 s物体停止，求物体与水平面间的动摩擦因数.
2007年2月28日凌晨1时55分左右，从乌鲁木齐驶往阿克苏的5806次列车遭遇特大沙尘暴，11节车厢被狂风掀翻，共有4人死亡，30多人受伤。这次天气过程( )
If you really want yourself to be in good health, you must_______ always _________ so much. A. not, be smoking B. not, have smoked C. not, to smoke D. be not, smoking
——You know, I’ve become a Hollywood star. ——Really? _______. A. It’s an obvious fact B. You have yourself to thank C. I suppose you are right D. Congratulations
He is very popular among his students as he always (试图使他们感兴趣) in his lectures.(make)
将7g某Cu、Ag合金与一定量的浓硝酸反应，合金完全溶解后放出的气体与标准状况下0.56L氧气混合后，通入水中恰好完全被吸收，则合金中铜的质量为(
---Will you go to watch the final game of the World Tennis Tournament to be held tomorrow afternoon? -- Of course．I think it _________an exciting game. A．seems B．promises
I’ve already told you that the fourth and last part of the article ______ the most difficult to understand. A. is B. was C. are
