71.
Many high school and college students are working as volunteers because .
A.
they have a lot of free time
B.
they can remember the problems of younger boys and girls
C.
they know how to play
D.
they like the work
E
During
recent years, floods and flash floods have caused billions of dollars in
damage. They are among the most common and widespread of all natural disasters.
Even more importantly, they're No.1 weather-related killer. A flood can happen
anywhere along the Mississippi, in New England, even in the desert.
The
following are some fascinating facts about floods and flash floods.
A
flood(commonly called
river flood)is high flow of water from a river or similar body of water,
happening over a period of time too long to be considered a flash flood.
Flooding is caused in many ways. Winter or spring rains, together with melting
snows, can fill rivers too quickly. Heavy rains from hurricanes or other
tropical(热带的)systems can also produce river flooding. The Mississippi
River Flood of 1993 was caused by repeated heavy rain from thunderstorms over a
period of weeks.
Flash
floods are quickly-rising floods which are usually the result of heavy rains
over a short period of time, often only several hours or even less. They can
also be caused by ice jams(冰塞)on rivers related to a
winter or spring melting, or occasionally even a dam break. The constant influx(汇集)of water finally
caused a great overflow to begin, powerful enough to sweep vehicles away, roll
big stones into roadways, uproot trees, level buildings, and knock bridges
down. The speed of the rising of water is the most frightening thing.
Remember:
Move to higher ground and stay away from low areas during heavy rain. Stay out
of flooded areas. Never allow children especially to play or walk in flowing
water. Never drive your car into water of unknown depths.