Do you know why different animals or pests(害虫) have their special colors? Colors in them seem to be mainly used to    1   themselves.
Some birds like eating locusts(蝗虫), but birds cannot    2  catch them. Why? It is because locusts change their   3   with the change of the colors of crops. When crops are green, locusts look    4 . But as the harvest time comes, locusts change into the same brown color    5  crops have. Some other pests whose colors are   6   plants are easily found and eaten by   7  . So they have to hide themselves for lives and appear only   8  .
If you    9 animals’ life, you’ll find the main use of colors is to protect    10  . Bears, lions and other animals  11  quietly through forests. They cannot be easily seen by hunters   12  their colors are much like the trees.
Colors are useful not only on the land, but also in the   13 . A kind of fish can   14  a kind of black liquid(液体) when they face danger. The liquid spreads over quickly, so they cannot be found by their enemies and can quickly swim away. That is   15  they can live safely though they are not strong at all. So colors are really useful to animals.

People live in different houses. You may know a wooden house or a paper house. But do you know a(n)    1   house?
In 2008, the first ice house in North America opens its    2   to welcome some visitors. The floors, windows and walls are all made of ice. It has ten bedrooms    3   twenty people can stay there each night. Visitors to the house    4   in ice beds, sit on ice chairs and eat from ice plates. Well, the toilets are not made of ice, of course.
It’s usually below zero so it is very    5   inside the house. However, do the visitors just sit there to    6   warm? No, visitors have to    7   special clothes. These can make    8  feel warm until morning.
Workers    9   about four weeks designing the ice house. Visitors can only stay in this ice house in winter. It isn’t    10   in hot summer. Because this house is so special, it is becoming popular with young people.

People live in different houses. You may know a wooden house or a paper house. But do you know a(n)  36  house?
In 2008, the first ice house in North America opens its  37  to welcome some visitors. The floors, windows and walls are all made of ice. It has ten bedrooms  38  twenty people can stay there each night. Visitors to the house 39  in ice beds, sit on ice chairs and eat from ice plates. Well, the toilets are not made of ice, of course. It’s usually below zero so it is very  40  inside the house. However, do the visitors just sit there to  41  warm? No, visitors have to  42  special clothes. These can make  43  feel warm until morning.
Workers  44  about four weeks designing the ice house. Visitors can only stay in this ice house in winter. It isn’t  45  in hot summer. Because this house is so special, it is becoming popular with young people.