---How long has the United Nations ________?
--- ______1945.A.e into existence; InB.been in existence; SinceC.been in existence; FromD.e into existence; For
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B解析这题考查动词的用法:因为和how long连用,要表示状态的动词be in existence,e into existence是短暂动词,不能和表示一段时间连用,第二空填since,可以和现在完成时连用。选B。