阅读理解。
When people want to know about the weather, they usually go to their radios, TVs, newspapers, or to the
Internet. However, you can also find many weather signs among wildlife, because of their highly developed
senses. Drops in air pressure (压力) produce an effect on small animals in many ways. Mice and deer are
good weather indicators. People who spend a lot of time outdoors have observed that, before a storm, field
mice come out of their holes and run around. Deer leave high ground and come down from the mountains.
Birds are especially good weather indicators because they also show the effect of a pressure drop in many
ways. For example, some birds become irritable (急躁的) and quarrelsome and will fight over a piece of bread.
Other birds chirp (叽叽喳喳) and sing just before a storm. It seems they know they won't get another chance
for an hour or two. Birds also seek safe places before a storm. You will sometimes see birds settling in trees
or gathering together on a wire close to a building. Pre-storm low pressure makes the air so thin that birds
have difficulty flying.
It is unusual to see many birds flying overhead in the summertime, rather than during the periods in the
spring or autumn. Watch for other weather signs if you see this. If they fly in the wrong direction, they may
be flying ahead of a storm.
By paying closer attention to some important signs in nature, we can become better prepared for any kind
of weather.
1. The word "indicators" in paragraph 1 probably means _____.
A. maps
B. services
C. signs
D. stations
2. There will be a storm if birds _____.
A. make more noise than usual
B. fly in different directions
C. come down from tall trees
D. share a piece of bread
3. How can birds sense the coming of a storm?
A. By feeling a drop in air temperature.
B. By noticing the change of wind directions.
C. By feeling a drop in air pressure.
D. By noticing the movements of other animals.
4. The best title for the text would be _____.
A. Signs of a Storm
B. Drops in Air Pressure
C. Animals'Sharp Senses
D. Nature's Weather Signs
＝10－5(mol/L)，由电荷守恒得：c(K＋)＋c(H＋)＝c(OH－)＋c(B－)，则c(Na＋)－c(B－)＝c(OH－)－c(H＋)＝(10－5－10－9)mol/L。