We can never expect         bluer sky unless we create         less polluted world.

A．a; a

B．a; the

C．the; a

D．the; the

引起脑梗死最常见的原因是（）

A.脑细小动脉硬化

B.脑动脉粥样硬化

C.脑动脉栓塞

D.脑出血

E.肿瘤