Is there any possible way to help them get rid of such a bad habit?

--- To tell the truth, it’s very hard. But we   on this problem trying to improve the situation.

A．worked

B．had worked

C．are working

D．had been working

MHC分子的功能不包括（）

A.参与对抗原的处理和呈递

B.约束细胞间相互作用

C.参与免疫应答的遗传调控

D.诱导同种淋巴细胞反应

E.激活补体