Not until they left school ____how much their teachers loved them and helped them.[ ]

A. that they realized            

B. had they realized  

C. when they would realize      

D. did they realize

期货交易的主要特点有（）。

A.实行保证金制度

B.实行日清算制度

C.实行佣金制度

D.交易对象是外汇期货合同

E.只能在交易所内进行