Order came that all the army supply ______ to the front before daybreak.

A．be sent

B．should send

C．were sent

D．should have sent

化学性食物中毒的最常见致病因素是（）。

A.有机磷农药

B.有机氯农药

C.铅中毒

D.汞中毒

E.N-亚硝基化合物中毒