免疫原性最强的物质是（）

A.脂多糖

B.多糖类

C.蛋白质

D.DNA

E.脂肪

— Jenny _____ have kept her words. Why did she change her mind?

— I think she _____ give more explanations to us.

[      ]

A. should; has to

B. should; had better

C. should; should

D. ought to; need