氨气____硫化钠____氢氧化钠____二氧化碳____氮气____次氯酸____．

Our science teacher asked us ____ we ____ ever been in a maglev train.

先化简： $(x-\frac{x}{x+1})÷(1+\frac{1}{x^2-1})$ ，然后在-1,0,1,2四个数中选一个你认为合适的数代入求值.

These simple ways can increase(增加)your popularity and win you more friends，so why not try them?
●PAYING ATTENTION TO OTHERS This will reduce any shyness you may have. You’ll be more relaxed and therefore more natural and fun. And you will get more good-people will love the fact that you’re paying attention to them while you don’t have to worry about what people think of you.
●LOOKING PEOPLE IN THE EYE Making eye contact is very important because it shows you’re interested in them. If you let your eyes wander(游移)or keep looking over their shoulders，people will feel slighted(轻视)，and they’ll like you less they would otherwise.
●ASKING QUESTIONS Doing this gives you two advantages，It shows other people that you are indeed paying attention to and that you consider what they are telling you important. Being sure to follow up when you’ve shared a conversation with someone about something important in his / her life，be sure to ask about it later. This shows that you listen and you care.
●MAKING AN EFFORT TO SMILE A smile means acceptance，and that makes people open up to you. Make a conscious(有意识的)effort(努力)one day to smile at the people you stay or work with and watch how well they respond (作出反应)to you；
●BEING RELIABLE(可靠的)People like those who help them，and they quickly begin to hate those who don’t.