下图所示的对称桁架中杆1和杆2的内力之间的关系是（     ）

<img src、"http://gansu.ouchn.cn/pluginfile.php/61593/question/answer/222251/8/246792/7-05-A.png" alt="" width="83" height="21">

<img src、"http://gansu.ouchn.cn/pluginfile.php/61593/question/answer/222251/8/246793/7-05-B.png" alt="" width="68" height="21">

<img src、"http://gansu.ouchn.cn/pluginfile.php/61593/question/answer/222251/8/246794/7-05-C.png" alt="" width="84" height="21">

<img src、"http://gansu.ouchn.cn/pluginfile.php/61593/question/answer/222251/8/246795/7-05-D.png" alt="" width="60" height="21">