We have been on duty for four hours and ____.     [ ]

A. now comes your tum                          

B. now does your tum come    

C. now your tum comes                          

D. comes now your turn

升高温度可以增加反应速率，主要是因为（）。

A.增加了反应物压力

B.增加了活化分子百分数

C.活化能增大

D.混乱度增加