When you want to go into the room, you s
题型:选择题
问题:
When you want to go into the room, you should _____ the door. [ ]
A. knock on
B. knocking on
C. knocks at
D. to knock at
When you want to go into the room, you should _____ the door. [ ]
A. knock on
B. knocking on
C. knocks at
D. to knock at