问题
选择题
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
答案
答案：A
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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
答案：A