Floods are second only to fire as the most common of all natural disasters.They occur almost everywhere in the world,resulting in widespread damage and even death.Consequently,scientists have long tried to perfect their ability to predict floods.So far,the best that scientists can do is to recognize the potential for flooding in certain conditions. There are a number of conditions,from deep snow on the ground to human error,which cause flooding.

    When deep snow melts it creates a large amount of water.Although deep snow alone rarely 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 on top of frozen or very wet ground,flooding is more likely to occur than when the ground is not frozen.Frozen ground or ground that is very wet cannot absorb the additional water created by the melting snow.Melting snow also contributes to high water levels in rivers and streams.

    Rivers that are covered in ice can also lead to flooding.When ice begins to melt,the surface of the ice cracks and breaks into large pieces.These pieces of ice move and float down the river,They can form a dam in the river,causing the water behind the dam to rise and flood the land upstream.If the dam breaks suddenly,then the large amount of water held behind the dam can flood the areas downstream too.

    Broken ice dams are not the only dam problems that can cause flooding.When a large human-made dam breaks or fails to hold the water collected behind it,the results can be devastating.Dams contain such huge amounts of water behind them that when sudden breaks occur,the great force of the water is like a great tidal wave.The dam waters can travel tens of kilometres,cover the ground in metres of mud and litter,and drown and crush every thing and creature in their path.

    Although scientists cannot always predict exactly when floods will occur,they do know a great deal about when floods are probably going to occur.Deep snow,ice-covered rivers,and weak dams are all strong conditions for potential flooding.

    The rules about how to talk, eat and sit, which are highly limited, are observed in most Western restaurants and homes. ____ Many Westerners have no idea how to act at the Chinese dinner table. No forks or knives for them to use! The Chinese host makes great, sweeping arm movements that go over large sections of the table, passing over both food and friends alike. ____ However, it leaves many foreigners at a loss for what to do.

    In my childhood home, dinner was enjoyed with low voices, and the topics that we could discuss were very limited. ____ If I had to leave the table to use the toilet, I had to excuse myself without mentioning what it was that I was going to do. “May I be excused, please? I need to wash my hands.” I would say. My mother would say, “Sure.” My father would often play a joke on me by saying, “____”

    As for eating, we did it quietly. No eating noises were allowed. Everything must be done as quietly as possible. If any sound was created by eating food or drinking, it would be considered as bad manners!

    ____He is to sit up straight with the recessive hand (usually the left) in one's lap holding a napkin while the dominant hand (usually the right) holds the fork or spoon. The only time one is allowed to have both hands on the table is when he is using a knife to cut something.

A. The scene is fantastic.

B. Your hands don't look dirty!

C. How one sits at the table is also prescribed.

D. Can't you think up a better excuse than that?

E. In general they were all strictly forbidden topics.

F. They're completely different from what we find here in China.

G. We were not allowed to talk about anything that made listeners uncomfortable.

将面团包在纱布中在清水中搓洗，鉴定粘留在纱布上的粘稠物质和洗出的白浆用的试剂分布是   （  ）