--You speak very good French!

---Thanks. I _________ French in Sichuan University for four years.

A．studied

B．study

C．was studying

D．had studied

引起心前区疼痛最常见的病因是（）

A.心脏神经官能症

B.肺栓塞

C.心绞痛、心肌梗死

D.急性心包炎

E.病态窦房结综合征