People around the world use different Ways to communicate. We communicate with each other not only through 1 but also through body language. Because body language is so 2. You'll have to know what yours means and what other people's means. Here are some examples 3 body language.

    If you drop down heavily and your head is down, this may 4 that you are sad or not happy. If you sit with a smiling face and look 5, you are expressing friendliness. A smile is a way of expressing friendliness and interest. But people 6 smile just to be polite. Friendliness and interest are expressed when a person's eyes 7 yours, especially when you're talking. A person who doesn't 8 you is showing that he is not interested in your talk.

    Hand gestures can mean a person is interested in the conversation. But repeated (重复的) movements, like hitting a pencil lightly against something again and again, often mean the person is 9 or not patient. Stay away from someone who 10 at you while talking with you — that person might be angry with you or feel better than you.

在下面①②③写恰当的语句，使整段文字语意完整连贯，内容贴切，逻辑严密。每处不超过18个字。

PM2．5是指空气中直径小于等于2．5微米的颗粒物。它能较长时间悬浮于空气中，其在空气中含量浓度越高，就代表①。虽然PM2．5只是地球大气成分含量很少的组成部分，②。与较粗的大气颗粒物相比，PM2．5粒径小，面积大，活性强，易附带有毒、有害物质（例如，重金属、微生物等），且在大气中的停留时间长，输送距离远，因而对③。