固定义齿受力后，因基牙有负重反应，故要求基牙（）

A.牙冠长而大

B.牙体组织健康

C.牙周条件好

D.咬合平衡

E.活髓牙

History is _______ a subject which only lets us know something in history..

A．not more than

B．less than

C．more than

D．no more than