慢性肺心病肺动脉高压的形成机制是（）

A.肺毛细血管床减少

B.长期反复发作的慢性炎症

C.肺细小动脉痉挛

D.血容量增多

E.血液黏稠度增加

When the bell rang, the students were all sitting on their own seats quietly and looking forward to        their new Chinese teacher.

A．have seen

B．be seen

C．see

D．seeing