My little sister doesn't like playing basketball.  So it         _ hers.              [ ]

A. can't be            

B. must be            

C. mustn't be

两根材料和约束相同的圆截面细长压杆，ι₂=2ι₁，若两杆的临界力相等，则d₁/d₂为（）。

A.3√2

B.√2

C.(3/2)√2

D.1/√2