在与同学的交往中，如果封闭自己[ ]

①会使自己的人际圈越来越小

②就不能使同学们了解自己，得不到同学们的帮助

③会减少自己的信息来源，不利于自己健康成长

④会使自己排除各种干扰，进步更快

A．①④

B．②④

C．①③④

D．①②③

I didn't _____ you were going to leave _____ 3 o'clock. [ ]

A. find; at

B. realize; until

C. remember; before

D. tell; after