Every time he tries to break a record, he reaches a point ________ he feels he can not physically

do any more.[ ]

A. why  

B. which

C. as  

D. where

呼吸量的增加必然导致()的增加。

（A）有害气体 

（B）体温 

（C）有害空间 

（D）呼吸阻力