-3的倒数是 ( )
A:3
B:-13
C:-3
D:13
当你屈肘时,肱二头肌和肱三头肌的状态分别是( )
—— How much did you _______ on the shirt?——Five hundred yuan.——Oh, It's ______ expensive. I can't take it.
直流电动机的缺点之一是 ____.
作为系统的边界,细胞膜在细胞的生命活动中有多种功能。右图模型主要表明了细胞膜的何种功能