It was not until the supreme lending crisis (次贷危机)had caused great damage to the American

financial system ______ Americans realized the severity (严重性) of the situation. [ ]

A. which          

B. that              

C. what            

D. when

已知。2273K时，反应N₂(g)+O₂(g)=2NO(g)的=0.100。2000K时，若p(NO)=p(N₂)=10kPa，p(O₂)=100kPa，反应向()方向自发进行。