引起肾综合征出血热的病原是（）。

A.汉坦病毒

B.登革病毒

C.新疆出血热病毒

D.黄热病毒

E.Lassa病毒

This cake is very sweet. You _________ a lot of sugar in it.  

A．should put

B．could have put

C．might put

D．must have put