Giải chi tiết Read the passage and circle the letter A, B, C, or D to indicate the correct answer to each of the,following questions.,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.,Question 21. Which can be the best title for the passage?,A. The nature of radar B. History of radar C. Alternatives to radar D. Types of ranging,Question 22. According to the passage, the distance between a radar set and an obiect 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

Question

Giải chi tiết Read the passage and circle the letter A, B, C, or D to indicate the correct answer to each of the,following questions.,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 &quot;radar&quot;,,in fact, gets its name from the term &quot;radio detection and ranging&quot;. &quot;Ranging&quot; 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.,Question 21. Which can be the best title for the passage?,A. The nature of radar B. History of radar C. Alternatives to radar D. Types of ranging,Question 22. According to the passage, the distance between a radar set and an obiect 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 &quot;ranging&quot; 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

Accepted Answer

Question 21. The best title for the passage is:

A. The nature of radar.

Question 22. According to the passage, the distance between a radar set and an object can be determined by:

D. the time it takes for the radio waves to produce echoes and bounce off the object.