<img src、"http://huagong.ouchn.cn/pluginfile.php/188255/question/answer/151162/3/838712/22.png" alt="" width="44" height="27">
<img src、"http://huagong.ouchn.cn/pluginfile.php/188255/question/answer/151162/3/838713/23.png" alt="" width="55" height="35">
<img src、"http://huagong.ouchn.cn/pluginfile.php/188255/question/answer/151162/3/838714/24.png" alt="" width="244" height="41">
、<span>一定为零</span>