試題分析:因?yàn)橛?img src="http://thumb.zyjl.cn/pic2/upload/papers/20140824/201408240332005381019.png" style="vertical-align:middle;" />.因?yàn)?img src="http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824033200538637.png" style="vertical-align:middle;" />.即
.又因?yàn)楹瘮?shù)
在定義域內(nèi)是遞減的所以解得
.又因?yàn)?img src="http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824033200600782.png" style="vertical-align:middle;" />.因?yàn)?img src="http://thumb.zyjl.cn/pic2/upload/papers/20140824/20140824033200600442.png" style="vertical-align:middle;" />可解得
.所以
.故選C.