(2009福州市高中毕业班第一次单科质量检查) Why didn’t you tell me there was no class today? You _____ me about it earlier.

A．ought to have told

B．should tell

C．should have been told

D．ought to be told

计算题：某井压裂设计加砂10方，砂比25%，排量为4方/分。问需要多少方混砂液？加砂需用几分钟？