用第一换元法求不定积分，则下列步骤中正确的是（　）．

<img src、"http://oss.ouchn.cn/ddzx/N601/gongxue/jjsx/img/2-3/image033.png" alt="" align="middle">

<img src、"http://oss.ouchn.cn/ddzx/N601/gongxue/jjsx/img/2-3/image034.png" alt="" align="middle">

<img src、"http://oss.ouchn.cn/ddzx/N601/gongxue/jjsx/img/2-3/image035.png" alt="" align="middle">

<img src、"http://oss.ouchn.cn/ddzx/N601/gongxue/jjsx/img/2-3/image036.png" alt="" align="middle">