Câu hỏi:

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 from 31 to 35.

Over the last twenty years, security cameras (31)       become a part of daily life. They are in elevators, parking garages, even on the streets. Of course, a security camera is only useful if there is a guard (32)        it, and there are definitely more cameras in our world than there are guards. That is why many of the security cameras you see are not actually (33)        . They look like cameras, but they do not actually work. They are only there to make people think that they are being watched. Since (34)       don’t know which cameras are real and which one are not, the fake cameras work as well as the real (35)       .     

Over the last twenty years, security cameras (31)       become a part of daily life.