Read the passage and choose the best answer.
A pilot cannot fly by sight alone. In many conditions, such as flying at night and landing in dense fog, a pilot must use radar, an alternative way of navigating. Since human eyes are not very good at determining speeds of approaching objects, radar can show a pilot how fast nearby planes are moving. The basic principle of radar is exemplified by what happens when one shouts in a cave. The echo of the sounds against the walls helps a person determine the size of the cave. With radar, however, the waves are radio waves instead of sound waves. Radio waves travel at the speed of light, about 300,000 kilometers in one second. A radar set sends out a short burst of radio waves. Then it receives the echoes produced when the waves bounce off objects. By determining the time it takes for the echoes to return to the radar set, a trained technician can determine the distance between the radar set and other objects. The word “radar”, in fact, gets its name from the term “radio detection and ranging”. “Ranging” is the term for detection of the distance between an object and the radar set. Besides being of critical importance to pilots, radar is essential for air traffic control, tracking ships at sea, and for tracking weather systems and storms.
According to the passage, the distance between a radar set and an object can be determined by _______.
A. the time it takes for a burst of radio waves to produce echoes when the waves bounce off the object
B. the term “ranging” used for detection of the distance between an object and the radar set
C. the time it takes for the radio waves to produce echoes and bounce off the object
D. the time it takes for the echoes produced by the radio waves to return to the radar set
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Giải thích: Dựa vào “The echo of the sounds against the walls helps a person determine the size of the cave.”
Đáp án D
The cost of living has ___________ over 10 percent in the past years.
The 6 - year - old boy resembles to his mother some what more than does his older brother.
As soon as we’ve finished supper, we’ll all go to downtown to see our friends.
Now men and women remain single longer than they once ___________
A thirteen-year-old does not spend as much money as his parents suspect - at least not (1) ………….the findings of recent survey, Money and Change. The survey (2) ……….. three hundred teenagers, 13-17 years old from (3) …………. Britain.
By the time they (4) ………… their teens, most children see their weekly allowance rise dramatically to an amazing national average of $5.14. Two thirds think they get (5) …………. money but most expect to have to do something to get it.
Although they have more cash, worry about debt is (6) ………….. among teenagers. Therefore, the majority of children make an effort to save for the future.
Greater access to cash (7) ……………. teenagers does not, however, mean that they are more irresponsible as a result. The economic recession seems to have encouraged cautious attitudes to money, even in the case of children at these ages. Instead of wasting what pocket (8) …………… they have on sweets or magazines, the teenagers who took (9) …………. in the survey seem to respond to the situation by saving more than half (10) …………. their cash.
Điền vào số 2
She shouted at him, "Go away, I don't want to see you no longer."
Dress ___________ when you go for an interview. Don’t wear your Jeans.
