“笑气”（N₂O）在医学上曾被用作麻醉剂，其中N元素的化合价是（）

增加：在缺词处加一个漏字符（^），并在其下面写出该加的词。

删除：把多余的词用斜线（\）划掉。

修改：在错的词下面画一横线，并在该词的下面写出修改后的词。

注意：1.每处错误及其修改仅限一词。2.只允许修改10处，多者（从第11处起）不计分。

    Last Saturday I went to the library as usually. At about noon, I was enjoying my reading near a lake while suddenly I hear someone crying for help. I went up to see what was happened. I was shocking to find a little child struggling in the water in the distance while many peoples were standing by without doing anything. Without any hesitation, I had pushed through the crowd as I took off my coat, but jumped into the water quickly. I managed to reach him and carried him back to safety. To his great relief, the kid was saved.

    I am proud what I did. I hope everyone can give a hand when someone else is in need.

2014年12月12日，南水北调中线一期工程正式通水，来自汉江上的一库清水蜿蜒北上，泽被北方。在这背后，是库区群众的付出：以前，为了给南水北调工程水源地湖北丹江口水库腾地蓄水，库区34万群众移民，从此故乡是“他乡”；如今，为了保护这一库清水，库区群众不得不舍弃唯一的致富“饭碗”网箱养鱼。“南水北调，服从国家大局嘛，希望北方人民珍惜用水！”库区群众说。这启示我们(       )