120阀紧急制动位时，紧急活塞两侧形成很大反差，紧急活塞下移顶开（），继而打开紧急放风阀使制动管压力迅速排出大气。

A.主阀加速缓解阀止回阀

B.紧急阀

C.先导阀

D.局减阀

选择与句中画线部分意思相同或相近的词或短语。

There is a wind today. [ ]

A. It's very windy

B. It is cloudy

C. It is windy

D. It will be windy