He must have had an accident , or he        here for class then .

A．had to be

B．should be

C．would be

D．would have been

能将血浆中的二价铁氧化为三价铁的是 （）

A.铜蓝蛋白

B.球蛋白

C.铁蛋白

D.运铁蛋白

E.清蛋白