--Why does the lake smell terrible?

-- Because a large amount of water_______.

A．have polluted

B．is being polluted

C．has been polluted

D．have been polluted

关于肺血栓栓塞的定义，叙述错误的是（）

A.空气栓塞也可以导致肺栓塞

B.PTE就是肺栓塞

C.导致肺栓塞的血栓大多数来自深静脉

D.深静脉血栓形成与肺栓塞实质上为一种疾病

E.急性肺栓塞是导致肺梗死而出现临床症状