左心功能不全导致（）
A.肝瘀血
B.肾瘀血
C.肺瘀血
D.后腔静脉栓塞
E.肝硬化
参考答案：C
There is a big library in our school.There are more than twice________five years ago. [ ]
A. books than
B. as many books as
C. many books as
D. many more books than
单端反激变换电路一般用在（）输出的场合。
A.小功率
B.大功率
C.超大功率
D.中小型功率
