a + b = 180; b + c = 204; a + c = 186

=> (a + b) + (b + c) + (a + c) = 180 + 204 + 186

=> a + b + b + c + a + c= 570

=> 2 x (a + b + c) = 570

=> a + b + c = 570 : 2

=> a + b + c = 285

=> a = 285 - 204 = 81

=> b = 180 - 81 = 99

=> c = 285 - 81 - 99 = 105

Choose the best option.

Computer is one of the most important ....... of 20th century.

A. inventions

B. invent

C. inventor

D. inventing

Mark the letter A, B, C, or D to indicate the word(s) CLOSEST in meaning to the underlined word(s) in each of the following questions.

In the past, a lot of countries denied having contributed to global warming.

A. agreed

B. refuted

C. approved

D. avoided