An excellent teacher is believed to be one who cares about his students but asks for nothing __________.

A．in turn

B．in short

C．in return

D．in general

喘证最主要的特征为（）.

A.呼吸困难

B.鼻翼煽张

C.张口抬肩

D.不能平卧

E.咳吐痰涎