The thief was noticed _____the office building by the back door on the screen.A.enterB.enter intoC.to enterD.to enter into
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C解析考查感官动词。See/notice/watch/hear/make等词，后跟不带to的不定式作宾补，但在被动语态中，要还原to。即，sb. be seen/noticed/watched/heard/made to do sth.。故选C。