What is the main topic of the passage?

Câu hỏi :

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.

 

In 1752, Benjamin Franklin made his textbook experiment with a brass key and a silk kite that he flew in a thunderstorm to prove that lightning and electricity are the same thing. In 1920, a kite-flying championship for families and individuals was held in London. These two seemingly unrelated events underscore the fact that kites can be flown for both pleasure and scientific purposes. For example, in the 1800s weather bureaus flew kites to record temperature and humidity at certain altitudes. On one occasion, ten kites were strung together and flown at a height of four miles to lift men and carry cameras aloft.

The kite’s ability to fly depends on its construction and the way that its line is attached. The familiar diamond - shaped kite flies when its covered face is aligned against the wind flow. The line attached to the nose of the kite pulls it into the wind, thus creating the necessary angle for the lift force. If the kite’s construction and the angle of the air stream are correct, the kite will encounter greater pressure against its face and lower pressure against its back. The difference in the pressure creates a lift that causes the kite to rise until it hangs level from its bridle. Its angle against the wind should be sufficiently large or small to create maximum lift to overcome both drag and gravity. The towing point to which the line is attached is important because it sets the kite’s angle relative to the air flow. Although the kite must be headed up and into the wind with a velocity of 8 to 20 miles per hour, it can maintain its position through a tail, a rudder, a keel, vents, or tassels.

Question 15: What is the main topic of the passage?