A:重力、弹力和下滑力
B:重力和弹力
C:重力和下滑力
D:重力、压力和下滑力
保障我国人民当家作主的根本政治制度是( )
Read and Judge.读短文,判断表格中的单词是对是错。
Hello. I am a boy. My name is Jack. I carry my bag and go to school. 1 have a pendl-case. Open my pencil-case. I have a pen, pencil, and shmpener ( 削笔刀). And the books are in the bag.
已知BP→=2PA→,若OA→=a→,OB→=b→,则OP→=( )(用a→,b→表示)