It’s an international school,_____of the students _____ from foreign countries.

A．two-third; are

B．second-thirds; is

C．two-thirds; are

D．two-three; is

引起急性主动脉瓣关闭不全的病因中，最常见的是()

A．风湿性心脏病

B．感染性心内膜炎

C．梅毒性主动脉炎

D．二叶主动脉瓣畸形

E．主动脉黏液样变