—I haven’t seen Tom for years. Any news about him?

—He          in a toy factory for two years. Now he’s working on a farm.

A．works

B．worked

C．has worked

D．had worked

中和抗体抗病毒的主要作用机制是阻止病毒（）

A.吸附细胞

B.基因表达

C.脱壳和穿入

D.生物合成

E.释放