已知点（1,3）为曲线的拐点，则a,b分别等于(    )

A、<p><span style="font-family: 微软雅黑, 'Microsoft YaHei';">1,2</span><br></p>

B、<p><span style="font-family: 微软雅黑, 'Microsoft YaHei';">1,-1</span><br></p>

C、<p><img src="http://oapi.open.com.cn/api/core/file/gofile.do?id=PIgucksTEMP20160910022722447.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=PIwytlpTEMP20160910022736480.png&amp;appkey=5da97a028134420c84123474e7e59e93" title="blob.png" alt="blob.png"></p>