The Titanic, the biggest ship of its day, ____ unsinkable, but it sank on its first voyage in 1912.

A．thought

B．was thought

C．thought it

D．was thought it

下列对免疫说法错误的是 [ ]

A．免疫可以抵抗抗原的侵入              

B．免疫总是对人体有益的

C．免疫能识别体内的异常细胞             

D．免疫是人体的一种生理功能