— May I speak to Mrs. Black?
— Sorry, mum can't come to the phone now. She a shower.
A:has
B:had
C:is having
D:was having
如图,一块厚度、密度均匀的长方形水泥板放在水平地面上,用一竖直向上的力,欲使其一端抬离地面。则( )
只要认真的测量,误差是可以避免的.(判断对错)