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_____ at the door before entering please.
A. Knocked B. To knock C. Knocking D. Knock
______ at the door before entering please.
A．Knocked B．Knock C．Knocking D．To knock
A．Knocked
B．To knock
C．Knocking
D．Knock
________ at the door before entering, please.
at the door before entering,please.?
A.Knocked B.To knock
C.Knocking D.Knock