bootcss ie 浏览器 （7-9）样式无效，怎么解决啊 ，求大神

/*!
* Bootstrap v2.3.2
*
* Copyright 2013 Twitter, Inc
* Licensed under the Apache License v2.0
* http://www.apache.org/licenses/LICENSE-2.0
*
* Designed and built with all the love in the world by @mdo and @fat.
*/