Na－CMC在水基钻井液中具有（）作用。
A、降粘
B、絮凝
C、乳化
D、增稠
参考答案：D
---________ have you studied in this school?
--- For about two years.
A．How often
B．How long
C．How much
D．How many
转盘道岔能够转动（）度。
A、90
B、180
C、270
D、360
