Read the following passage and mark the letter A, B , C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks.

Speech is one of the most important (13) ______ of communicating. It consists of far more than just making noises. To talk and also to (14) ______ by other people, we have to speak a language, that is, we have to use combinations of (15) ______ that everyone agrees to stand for a particular object or idea. Communication would be impossible if everyone made up their own language.

Learning a language properly is very (16)______ . The basic (17) ______ of English is not very large, and not only about 2,000 words are needed to speak it quite (18)______. But the more idea you can (19) ______ the more precise you can be about their exact meaning.

Words are the (20) ______ thing we use in communicating what we want to say. The way we (21)______ the words is also very important. Our tone of voice can express many emotions and (22) ______ whether we are pleased or angry, for instance.

Điền vào ô 22

A. know 

B. show 

C. ask 

D. understand

Tính:  cos 225 ° ,   sin 240 ° , cot - 15 ° ,   tan 75 °