vì trong không khí có nhiều chất khí khác nhau mà chất khí gây cháy là oxi nên tất nhiên chấy trong không khí sẽ chậm hơn trong oxi

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.

          Although speech is the most advanced form of communication, there are many ways of communicating without using speech. Signals, signs, symbols, and gestures may be found in every known culture. The basic function of signal is to impinge upon the environment in such a way that it attracts attention, as, for example, the dots and dashes of a telegraph circuit. Coded to refer to speech, the potential for communication is very great. Less adaptable to the codification of words, signs also contain meanings in and of themselves. A stop sign or a barber pole conveys meaning quickly and conveniently. Symbols are more difficult to describe than either signals or signs because of their intricate relationship with the receiver's cultural perceptions. In some cultures, applauding in a theater provides performers with an auditory symbol of approval. Gestures such as waving and handshaking also communicate certain cultural messages.
          Although signals, signs, symbols, and gestures are very useful, they do have a major disadvantage in communication. They usually do not allow ideas to be shared without the sender being directly adjacent to the receiver. Without an exchange of ideas, interaction comes to a halt. As a result, means of communication intended to be used for long distances and extended periods must be based upon speech. Radio, television, and the telephone are only a few

What does the author say about speech?

A. It is the only true form of communication.

B. It is the most advanced form of communication.

C. It is necessary for communication to occur.

D. It is dependent upon the advances made by inventors.

To preserve that ________, it was necessary to preserve the people that had created it.

A. civilize             

B. civilization      

C. Civility            

D. civil