完形填空。
    Do you know? There is one language 1 in every country in the world. People, young or old, short or tall, thin or fat, use it very often. It is everybody’s second2 . It is very easy to3, though you can't hear it. It is a sign language.
    When you wave(挥手) to a friend on the street, you are 4sign language. When you 5 up your hand in class, you are saying, “Please ask me, I think I know the answer,” or “I have some questions to6.” When you smile at someone, you mean to be 7to him. When you put your forefinger(食指) in front of your mouth, you mean, “8 quiet, please.” When a policeman wants to 9cars or buses, he raises his right arm. Sign language is very useful in quiet places or places 10 of noise. It is different from body language.

材料一：在飞机场，人们排队进行安全检查；在服装厂，纺织工人按操作规程工作；在十字路口，行人、自行车、机动车各行其道；在公共场所，人们保持安静。

材料二：马女士抱着熟睡的孩子在候车室候车。邻座的一位男士不停地大声打手机。“孩子睡着了，请你小声点。”“打手机是我的自由！”“‘自由’也不能损害其他人的自由和权利呀！”

汽油机是热机中的一种，如图所示，是汽油机的____ 冲程，此过程是将内能转化为____ 能．热机的发展和应用推动了社会的快速发展，但同时又对环境造成了一定程度的污染，还要消耗大量的不可再生能源，对此请你写出一条合理建议：____ ．

典型的营群体生活的动物群体中，个体之间的关系是