[单项选择](Neither) rain (nor) sleet nor snow (keep) the mailman from his (appointed) rounds.
A. Neither
B. nor
C. keep
D. appointed

[单项选择](Neither) rain (nor) sleet nor (keep) the mailman from his (appointed) rounds.
A. Neither
B. nor
C. keep
D. appointed

[单项选择]The sharp rise of the snow geese population is mainly caused by ______.


A. lack of natural enemies
B. great care of wildlife preservationists
C. favorable conditions in their winter habitat
D. changes in their migration patterns

[单项选择]The heavy snow could not keep us （　） going out to work.
A. on
B. up
C. upon
D. from

[单项选择]The heavy snow could not keep us ______ going out to work.
A. from
B. on
C. upon
D. up

[单项选择]In spite of the heavy snow and hard rain, the buses still ran on. ______.
A. list
B. plan
C. arrangement
D. schedule

[单项选择]Acid rain


A. immediately kills trees and affects aquatic life in lakes and rivers.
B. deposits various metals iron, mercury, aluminum into the soil.
C. kills forests by weakening them and reduces fish populations.
D. releases sulfur dioxide, nitrogen oxide and into the atmospher

[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