哪项胎儿发育指数可以提示有胎儿宫内发育迟缓的可能：

A．＜-2

B．＜-3

C．＜-l

D．＞1

E．＞3

It costs      __    to travel by air as by train.      [ ]

A.  more three times    

B.  as much tree times  

C.  three times as much