阅读短文B，回答问题。
We are in a world full of competition. Our parents compete（竞争）with others in their offices, our brothers and sisters compete with others in their colleges, and we compete with our classmates in school. Many of us give up in the face of competition. Why can't we do better than others? One important reason is that we have no self -confidence.
In fact, everyone is born equal. You can do what others do. Although your classmates may be better than you in some ways, you may be better than them in other ways. So everyone has his or her own advantages. Don't look at things from a single point of view. Try to discover your own advantages, and believe that you can do better than others in those ways.
Competition is not so terrible. Don't be afraid of it. And don't be afraid of those classmates who are better than you. Remember that the first step to success is self-confidence. Believe in yourselves, and you will be successful.
2NH3(g)，△H<0，达到平衡时，当单独改变下列条件后，有关叙述错误的是（ ）