在一定体积的密闭容器中通入a mol NO和b mol O₂，反应容器内氮原子个数与氧原子个数之比为（ ）

A. a/b              B.a/(a+b)           C.a/(a+2b)           D.a/2(a+b)

A.a/b                                                             

B.

C.                                                     

D.