It is worth considering what makes “convenience” foods so popular, and_______ better ones of your own.

A．introduces

B．to introduce

C．introducing

D．introduced

儿童呛咳的主要原因是（）

A.支气管淋巴结肿大

B.肺结核

C.支气管肺癌

D.肺气肿

E.异物吸收