Allen wanted to know ____ after it got out of the UFO.

A．what is the alien doing

B．what the alien would do

C．where would the alien go

D．where the alien is going

常用的不可逆性水胶体印模材料，其主要成分是（）

A.硫酸盐基；

B.琼脂基；

C.硅橡胶基；

D.藻酸盐基；

E.树酯。