螺杆式低压空压机的油过滤器的作用（）
参考答案：过滤冷却油中的杂质及污物
Our foreign English teacher Shirley has a gift for creating an atmosphere for her students _________ allows them to communicate freely with each other.
A．which
B．where
C．what
D．who
对于空分塔，回流比通常用（）表示。
A.G/g
B.g/G
C.x/y
D.y/x
