朗格汉斯细胞（Langerhans cell）具有的功能有（）

A.呈递抗原

B.免疫耐受

C.免疫监视

D.免疫调节

E.合成抗体

－So hard   in the past few months that he has got an A in the Mid－term English Exam.

－I can see that only a few students   for it.

A．has he worked; has the teacher praised.

B．has he worked; the teacher has praised.

C．he has worked; the teacher has praised.

D．did he work; has the teacher praised.