生理情况下,1ml血含铁量为()
A.0.25mg
B.0.5mg
C.1mg
D.1.5mg
E.2mg
参考答案:B
–I drove to Zhuhai for the air show last week.
-Is that you had a few days off?
A.why
B.when
C.what
D.where
作用在一个物体上的两个力,大小分别是60N和80N,如果它们的夹角是90°,则这两个力的合力大小是( )
A.20N
B.70N
C.100N
D.140N