下列物质的用途，主要由化学性质决定的是（　　）

B

    You may know the English letters A, B and C, but do you know there are people called "ABC"? You may like eating bananas, but do you know there are people called "banana persons"? If you don't know, I will tell you about it. They are some Chinese people like you and me, but they aren't in China. Why do people call them like that?

    If we call somebody an ABC person, we mean he or she is a Chinese but was born in America. Sometimes, people also call them "banana persons". A banana is yellow outside and white inside. So if somebody is a "banana person", he or she is "white" inside and "yellow" outside. By saying that, we mean he or she has yellow skin(皮肤) but does things in an American way. "Banana persons" were born in America and they live in America for a long time, so they think like Americans and do things like Americans. However, these people still have Chinese blood(血统). Their parents, grandparents or even great-grandparents are from China. They all have black eyes and black hair, so they look like us, Chinese people.

    There are many famous "banana persons" in America. They do very well in America and they are really great in their own fields.

某种冰箱经两次降价后从原来的每台2500元降为每台1600元，求平均每次降价的百分率为____．

动物在陆地上的运动方式多种多样，无论是行走、奔跑还是跳跃，都扩大了陆生动物的____，有利于它们获得食物和____。