单选题 12.  Be careful; Samantha accidentally knocked ______ her mug of coffee and hasn't had a chance to mop up the mess.
【正确答案】 A
【答案解析】 选项A正确，knock over意思是“打翻，撞到”。选项B错误，knock back意思是“很快地喝掉”。选项C错误，knock out意思是“击倒，使不省人事”。选项D错误，knock through意思是“拆除墙壁，打通隔墙”。