题目

纯净的水呈中性，这是因为               （    ） A．纯水中C（H+）=C（OH-）               B．纯水PH=7 C．纯水的离子积KW=1．0×10-14                 D．纯水中无H+也无OH- 答案：AKnowing how and when to say goodbye is often difficult, even in informal situations. 1. It will help you maintain your relationships and let people know you care. It’s also easier than it seems sometimes. Read on to learn how to recognize opportunities and predict others’ needs when you leave.Recognize when to leave. When you’re at any kind of party, or even a one-on-one conversation，it can be difficult to get away. Learning to recognize good opportunities to leave will make a goodbye much easier. 2. If more than half the people have left, it might be a good time to leave.3. Overstaying your welcome is rude, but it can often be difficult to distinguish. People don’t like telling you that they’d like you to leave，so try to watch for signals. This may be some other family members starting to check their watch or even pack up or the fact that there is hardly anyone left.Make plans to see each other again. Saying, “See you at school tomorrow” or “Can’t wait to see you again at Christmas” keeps the goodbye light and focused forward. If you haven’t already made plans, use it as an opportunity to make them.4.Tell the truth. It can be tempting to come up with a “good excuse” when you’re ready to leave. You don’t need to. 5. It doesn’t need to be any more complicated than that.A. Watch body language.B. Leave when you want.C. Notice if the crowd seems to be decreasing.D. Even saying, “See you soon” suggests just that.E. If you want to leave, just say, “I’ll be going. See you later.”F. But learning to say goodbye appropriately is a must-have skill.G. Don’t make plans with people you don’t really care about saying goodbye to.