[单项选择]

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 average size of a cloud droplet is only 0. 0004 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 mo
A. unpredictable
B. perplexing
C. independent
D. abnormal

[单项选择]

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 average size of a cloud droplet is only 0. 0004 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 mo
A. They never occur.
B. They are not affected by the force of gravity.
C. In still air they would fall to earth.
D. In moving air they fall at a speed of thirty-two miles per hour.

[单项选择]What makes rain fall

[单项选择]In what sense was Niagara Falls thought to embody religious qualities

[单项选择]What is Sam suffering from


A. Cold.
B. Lung.
C. Cough.
D. Congestion.

[单项选择]What distinguishes Shakespeare from the other English dramatists who also used well- known English history and old legends as sources


A. His recreation of familiar tales.
B. His competence in foreign languages.
C. His own experience as an actor.
D. His Roetic passion:

[单项选择]What distinguishes morphology from syntax deals with the rules governing the combination of
A. words into phrases and sentences.
B. sounds into patterns and words.
C. meanings into passages and system.
D. words into branches and language.

[单项选择]What did people do to solve the problem of rain lack around Chad Lake


A. They moved out of this area.
B. They drew water from Lake Chad.
C. They carried water from other areas.
D. They utilize sea water near this are