潜水艇充满水时,可以悬浮在海水中静止不动.此时,它在竖直方向上受到_______ 力和_________力的作用,这两个力的合力是_________ 。
重;浮;零
It being Sunday, rather than ______ at home, I preferred _______.
A stay; to travel B to stay; to travel C stay; travel D to stay; traveling
“大有大成,小有小成”是()教学原则具体运用的结果。
A.自觉积极性
B.启发性
C.巩固性
D.因材施教