Schools that serve healthier food, offer nutrition education and reward students for good eating habits can make a major        in preventing childhood obesity.

A．mistake

B．sense

C．impression

D．difference

干酪根演化成石油的主要控制因素是（）。

A.时间、温度、压力

B.浓度、温度、压力

C.浓度、压力、时间

D.温度、时间、催化剂