What happen作主语可以等于什么?

A rabbit is running into his hole. You may ask, “What happened?”
Well, when a rabbit sees something dangerous, it runs away. Its tail moves up and down as it runs. When other rabbits see this tail moving up and down, they ran, too. They know there is danger. The rabbit has told them something without making a sound. It has given them a signal .
Many other animals use this kind of language. When a bee finds some food, it goes back to his home. It can’t tell the other bees where the food is by speaking to them, but it does dance in the air. This tells the bees where the food is.
But animals say things by making sounds. A dog barks, for examples, when a stranger comes near. A cat purrs(发出呼噜呼噜的声音) when pleased. Some birds make several different sounds, each with its own meaning.
But human beings have something that no animals have---- a large number of words about things, actions, feelings or ideas. We are able to give each other information to tell or inform other people what is in our mind or how we feel. By writing words down we can remind ourselves of the things that have happened, or send messages to people far away. No animals can do this. No animals has the wonderful power of language.
No one knows how man learned to make words. Somehow he learned to make them. As centuries went by, he made more and more new words. This is what we mean by language.
People in different countries made different kinds of words. Today there are about fifteen hundred different languages in the world. A very large English dictionary, for examples, contains four or five hundred thousand words. But we don’t know all these. The words we know are called vocabulary. We should try to make our vocabulary larger. Read as many books as possible. When we met a new word, look it up in the dictionary. A dictionary is the most useful book.
小题1:What’s the meaning of the underlined word?

A．标语

B．信号

C．唱片

D．图像

小题2:A dog can tell something__________.

A．by giving signals	B．by making different sounds
C．by purring	D．by barking

小题3:It has been proved that no animals are able to_________.

A．give the others information

B．express their actions and feelings with words

C．tell others how they feel

D．make different sounds, each with its own meaning.

小题4:Generally speaking, what we mean by “vocabulary” is_______.

A．all the words that we know	B．more and more words we use
C．all the words we need	D．the dictionary which contains thousands of words

小题5:What must we do in order to make our vocabulary larger?

A．Make more and more new words

B．look up some new words in a dictionary

C．learn more language

D．Try to read as many books as possible