——Fifty dollars for such a T-shirt! You _______ be joking!——I'm serious.It's made of silk.
A:must
B:need
C:may
D:can
计算:9+|﹣5|﹣(2﹣3)0.
一Wow!You play the violin very well,Bob.
— .
为测定一木块与木板间的动摩擦因数,同学甲设计了两种方案.
方案一:木板水平固定,通过弹簧秤水平匀速拉动木块,如图a;
方案二:木块固定,通过细线水平拉动木板,如图b.