问题
单项选择题
45号碳素钢的中的数字的含义（）
A.碳的含量
B.杂质的含量
C.铁的含量
答案
参考答案：A
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45号碳素钢的中的数字的含义（）
A.碳的含量
B.杂质的含量
C.铁的含量
参考答案：A
The world of out-of-doors is full of secrets. And they are so interesting that quite a lot of people are busy studying them. All around us are birds, animals, trees and flowers. The facts about how they 1 and grow are as interesting as anything could be. Do you know that one of the greatest presidents of the USA spent hours and hours 2 birds? A businessman who lives near New York city became so 3 in insects that he began to collect them. He now has more than one thousand different kinds carefully 4 in glass boxes. Come then with me, and I will help you find some of nature’s secrets. Let us go 5 through the woods and fields. Here we shall find how a rabbit tells the other rabbits that there is danger. We shall 6 a mother bear and her young ones as they look for 7 and get ready for winter sleep. We shall watch bees dancing in the air to let other bees know 8 they can find food. I will show you many other interesting things, but the thing that I can 9 you is to keep your eyes and ears 10 when you go out of doors. Nature tells her secrets only to people who look and listen carefully.
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