下列函数有界的是（  ）

A、<p><img src="http://oapi.open.com.cn/api/core/file/gofile.do?id=PIjifvyTEMP20160910105039358.png&amp;appkey=5da97a028134420c84123474e7e59e93" title="blob.png" alt="blob.png"></p>

B、<p><img src="http://oapi.open.com.cn/api/core/file/gofile.do?id=PIcuwaqTEMP20160910105052762.png&amp;appkey=5da97a028134420c84123474e7e59e93" title="blob.png" alt="blob.png"></p>

C、<p><img src="http://oapi.open.com.cn/api/core/file/gofile.do?id=PIonkytTEMP20160910105105143.png&amp;appkey=5da97a028134420c84123474e7e59e93" title="blob.png" alt="blob.png"></p>

D、<p><img src="http://oapi.open.com.cn/api/core/file/gofile.do?id=PIgytusTEMP20160910105116394.png&amp;appkey=5da97a028134420c84123474e7e59e93" title="blob.png" alt="blob.png"></p>