Be polite. You ________ talk to the old like that.

 [ ]

A. couldn't

B. needn't

C. mustn't

D. wouldn't

考虑诊断

A．伴性无丙种球蛋白血症

B．婴儿暂时性低丙种球蛋白血症

C．先天性胸腺发育不全

D．伴性高IgM血症

E．选择性IgA缺乏症