Scientists have long tried to be able to know more about floods。So far，the best that scientists can do is to recognize the conditions for flooding。
Although deep snow alone seldom causes floods，when it occurs together with heavy rain and sudden warmer weather，it can lead to serious flooding。If there is a fast snow melt (融化)on top of frozen or very wet ground，flooding is likely to occur。Melting snow also causes high water levels in rivers。Whenever rivers are already at their highest possible levels，heavy rains will result in the rivers’flooding the nearby land。
Rivers covered in ice can also lead to flooding。When ice begins to melt，it breaks into large pieces。These pieces of ice move and float down the river。They can block the river，causing the water to rise and flood the land up the river。If the ice dam(坝)breaks suddenly，the large quantity of water held behind it can flood the areas down the river too。
Broken ice dams are not the only problem that can cause flooding。When a large human—made dam breaks or fails to hold the water collected behind it，it will also cause serious damage。
Although scientists cannot always know when floods will occur，they do know a great deal about when floods are likely，or probably，going to occur。
What happens when ice dams break?
AThey may quickly block the river.
BThe ice covering the river may melt fast.
CA larger ice dam may soon be formed.
DThe areas down the river may be flooded.
Most 11-year-olds are just happy to have finished their first year of middle school. However, Tom is not like most kids. He did not go to elementary(小学), middle or high school but went straight to college at the young age of eight.
While Toms parents knew he was smart, they had never imagined putting him in college this young. However, when they tried to send him to a private(私立的)school at the age of six, he was turned down, because he was so smart that the school was afraid he would feel dull.
It turns out the school was right. After homeschooling the young boy for two years, the parents realized that he was ready for some real high-level courses. They came to East Los Angeles College, who agreed to take him in. However, until he proved himself, he could take only two courses—math and music.
Tom did not disappoint. He got A’s in both and hasn’t looked back since. Last week, he graduated as a top student. In fact, the young boy was so smart that he helped his fellow math students, some of whom were 10 years older than him.
While the world may cheer him as a genius(天才), his parents think he is just a normal boy who plays football and watches movies for children.
What did the parents do to Tom for two years before he went to college?
AThey sent him to a school in Los Angeles.
BThey let him attend music programs.
CThey hired a math teacher for him.
DThey taught him at home.