We all know that Bell        the telephone. It's very useful today.              [ ]

A. invented      

B. discovered              

C. found out    

D. found

中气不足，可引起的症状是（）

A.咳逆上气

B.恶心呕吐

C.头晕目眩、耳鸣

D.胃脘疼痛

E.脘腹有重坠感