分子筛孔比较均匀，只能吸附直径小于其孔径的分子。
参考答案：对
管道沟槽施工中，接口及铺管过程时，上、下沟槽不准攀登支撑。( )
. My father likes outdoor activities,_______ my mother prefers staying at home.
A．when
B．while
C．after
D．before
