（）在输水管道和给水管网中起分段和分区的隔离检修作用，并可用来调节管线中的流量或水压。
A、排气阀
B、泄水阀
C、止回阀
D、阀门
参考答案：D
He had studied Japanese for two years before he _____ English. [ ]
A. took over
B. took up
C. took on
D. took off
帕金森病早期的首发症状是（）
A、四肢肌强直
B、下肢肌强直
C、写字过小症
D、动作不灵活和震颤
E、行走呈前冲步态
