A、Words. B、Tone of voice. C、Sentence structures. D、Sounds. B四个选项均是名词(词组)，与语言有关。本题在最后，应在短文末尾处找答案。the main thing incommunicating指的

Speech is one of the most important ways of communicating. It consists of far more than just making noises. To talk and also to be understood by other people, we have to speak a language, that is, we have to use combinations of sounds that everyone agrees stand for a particular object or idea. Communication would be impossible if everyone made up their own language.
    Learning a language properly is very important. The basic vocabulary of English is not very large, and only about 2,000 words are needed to speak it quite well. But the more words you know, the more ideas you can express, and the more precise you can be about their exact meaning.
    Words are the main thing we use in communicating what we want to say. The way we say the words is also very important. Our tone of voice can express many emotions and shows whether we are pleased or angry, for instance.
19. What are used to stand for a particular object or idea when we speak a language?
20. What if everyone made up their own language?
21. What is also important besides the main thing in communicating?