缺词填空 先通读下面的短文，掌握其大意，然后根据短文内容和所给首字母，在空格内填入一个适当的词。所填单词在题后横线上必须完整写出。（本大题5分，每格0.5 分）
People use languages to communicate（交流）. Many animals don’t speak w___. But they have many other ways to communicate.
Have you seen fish swimming in a g____? Do they swim together because they can s_____ each other? That’s not true. They make s____ sounds, which can only be heard by fish, to keep swimming together. Birds are also good at u    sounds.
There are two m____ reasons for birds to use sounds. The first is that they use sounds when they l_____for “friends”. The other reason is that they make sounds to warn(警告) other birds that an enemy(敌人) is nearby. Birds are the b___ animals at communicating.
Frogs use songs to prevent(阻止) other animals getting into their “home”. Many animals in the sea make sounds to communicate in their s_____ groups.
Each animal makes sounds to express(表达) its o____ meanings.