In the U.S, ______a tip is thought to be polite when paying the bill.A.leaveB.having leftC.leavingD.being left
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C解析试题分析：句意：在美国当付账单时，留下一些小费被认为是有礼貌的。这里是动名词短语作主语，是通常的一种行为，所以用一般式就行，故选C。考点：考查非谓语动词的用法。
点评：本题难度适中。非谓语动词是近几年高考的热点，本题是对已学知识点的回顾，需要考生能够理解该题的语言环境，进而作出正确的判断。这里是动名词短语做主语。即学即练：An offer of a reward has caused many students in our school _________ actively in the petition.A. participate B. participatedC. participating D. to participate解析：D。句意：考查不定式短语作宾语补足语的用法。即：cause sb. to do导致某人做某事。