服用阿司匹林后出现呕血，其原因是（）

A.急性胃黏膜病变

B.消化性溃疡

C.急性胰腺炎

D.食管炎

E.胃黏膜脱垂

Li Fang is very busy，__________she’s always helping others with their lessons.

A．but

B．although

C．so

D．for