发动机冷却系水温低是由于（）。
A.风扇带打滑
B.水箱百叶窗未打开
C.节温器阀门开启过早
D.水箱和气缸水套内积垢太厚
参考答案：C
When the teacher walked into the classroom, the students ____ at once.
A．stopped to talk
B．stopped talking
C．stop to talk
D．stop to talking
通常用做钻井液处理剂的CMC的取代度在（）之间。
A.0.45~0.65
B.0.50~0.75
C.0.65~0.85
D.0.75~1.00
