求图示结构AB两点的相对线位移，虚设力状态为图（     ）

<img src、"http://sichuan.ouchn.cn/pluginfile.php/61593/question/answer/371610/3/246712/a.png" alt="" width="163" height="148">

<img src、"http://sichuan.ouchn.cn/pluginfile.php/61593/question/answer/371610/3/246713/b.png" alt="" width="163" height="148">

<img src、"http://sichuan.ouchn.cn/pluginfile.php/61593/question/answer/371610/3/246714/c.png" alt="" width="167" height="148">

<img src、"http://sichuan.ouchn.cn/pluginfile.php/61593/question/answer/371610/3/246715/d.png" alt="" width="167" height="148">