Mr. Smith asked Jenny some new words and let her to               on the blackboard.[ ]

A. write them down            

B. write it down  

C. write down it                

D. write down them

膀胱癌与膀胱内血凝块的鉴别要点是（）

A.前者为高回声，后者为低回声

B.前者为低回声，后者为高回声

C.后者可随体位改变而移动

D.前者形态规则，后者不规则

E.前者边界不清，后者边界清晰