A flood occurs(发生)when water is too much. This can happen in many ways. Most common is when rivers run out of their banks. Too much rain, a broken dam, ice in the mountains changing into water, or even an unfortunately placed dam can break down a river and send it spreading over the nearby land, called a floodplain(泛滥平原). Coastal flooding occurs when a large storm causes the sea to surge inland.
Most floods take hours or even days to develop, giving people enough time to prepare or leave. Others come quickly with little warning. These flash floods can be extremely dangerous, immediately turning a river into a thundering wall of water and sweeping everything in its path down.
Disaster experts divide floods into different types according to their possibility of occurring in a given time period. A hundredyear flood, for example, is an extremely large, harmful event that would theoretically(理论上) be expected to happen only once every century. But this is a theoretical number. In reality, this classification(分类) means there is a onepercent chance that such a flood could happen in any given year. Over recent ten years, possibly due to global climate change, hundredyear floods have been occurring worldwide pretty regularly.
Moving water has terribly harmful power. When a river rushes out of its banks or the sea drives inland, buildings poorly equipped to resist(抵抗) the water’s strength are no match. Bridges, houses, trees, and cars can be picked up and carried off.
When floodwaters become weak, the affected areas are often covered with mud(泥). The water and land can be polluted with dangerous materials, such as rubbish, industrial pollution, and dirty water. People of flooded areas can be left without power and clean drinking water, leading to dangerous waterborne diseases.
But flooding, particularly in river floodplains, is as natural as rain and has been occurring for millions of years.
1．What do we know about flash floods?
A．They happen only in floodplains.
B．They come quickly with little warning.
C．They are less dangerous than other floods.
D．They are caused by ice melting in the mountains.
2．The underlined word “surge” in Paragraph 1 probably means “________”．
A．become calm
B．rise and fall in waves
C．separate into more pieces
D．give one thing in exchange for another
3．Hundredyear floods have been occurring worldwide pretty regularly is perhaps because of ________.
A．global climate change
B．poor flood control projects
C．More and more trees' being cut down
D．many rivers becoming narrower
4．What does the passage mainly tell us?
A．How people can take measures to prevent floods.
B．How disaster experts divide floods into different types.
C．How people can deal with floods and survive from them.
D．How floods happen and the bad effects floods bring about.