在光滑的水平面上有a、b两球，其质量分别为 ma、mb，两球在 t 时刻发生正碰，并且在碰撞过程中无机械能损失，两球在碰撞前后的速度图象如图 1-6-6 所
It was a sunny day. A city man was driving along a country road with a new wagon（马车）and a beautiful pair of horses. He didn’t pay a lot of 16 to where he was going. Pretty soon he 17
All the visitors live on floor. A. two B. second C. the second
表皮损坏的蕃茄果实很快就会腐烂，这说明表皮是 ( ) A．机械组织 B．营养组织
Andy never wanted to go to bed on time．His parents had explained to him how important it was to go to bed early and get a good rest．But Andy paid no attention to them，and they didn't know wha
公有制为主体、多种所有制经济共同发展，是我国社会主义初级阶段的（ ） A．分配制度 B．经济制度的基础 C．基本经济制度
It’s raining hard. We have to stay at home __________ going fishing. A. in front of B. because of C. in need of D. instead of
给未授粉的番茄雌蕊柱头涂上一定浓度的生长素溶液，可获得无籽番茄。说明了（ ）A．果实发育与受精作用有关 B．果实发育与种子形
