— Never thought to meet you here at this time .

—            [ ]

A. Glad to see you.                

B. It's a small world.  

C. So did I.                      

C. Oh, haven't you?

在感染中，标志近期感染的抗体是（）

A.IgD

B.IgA

C.IgG

D.IgM

E.IgE