Question

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.

What makes it rain? Rain falls from clouds for the same reason anything falls to Earth. The Earth’s gravity pulls it. But every cloud is made of water droplets or ice crystals. Why doesn’t rain or snow fall constantly from all clouds? The droplets or ice crystals in clouds are exceedingly small. The effect of gravity on them is minute. Air currents move and lift droplets so that the net downward displacement is zero, even though the droplets are in constant motion.

Droplets and ice crystals behave somewhat like dust in the air made visible in a shaft of sunlight. To the casual observer, dust seems to act in a totally random fashion moving about chaotically without fixed direction. But in fact dust particles are much larger than water droplets and they finally fall. The cloud droplet of average size is only 1/2500 inch in diameter. It is so small that it would take sixteen hours to fall half a mile in perfectly still air, and it does not fall out of moving air at all. Only when the droplet grows to a diameter of 1/125 inch or larger can it fall from the cloud. The average raindrop contains a million times as much water as a tiny cloud droplet. The growth of a cloud droplet to a size large enough to fall out is the cause of rain and other forms of precipitation. This important growth process is called “coalescence”.

What can be inferred about drops of water larger than 1/125 inch in diameter?

A. They never occur.

B. They are not affected by the force of gravity.

C. In still air they would fall to the ground.

D. In moving air they fall at a speed of thirty-two miles per hour.

Answer 1

Đáp án là C.

Có thể suy ra điều gì từ những giọt nước có đường kín lớn hơn 1/125 inch?

A. Chúng không bao giờ xảy ra.

B. Chúng không bị ảnh hưởng bởi trọng lực.

C. Trong không khí tĩnh chúng sẽ rơi xuống mặt đất.

D. Khi di chuyển trong không khí chúng rơi với tốc độ 32 dặm/ giờ.

Dẫn chứng: Only when the droplet grows to a diameter of 1/125 inch or larger can it fall from the cloud