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.

When I was about 12 years old, I really wanted a new bike! I __36__ my parents my birthday wish, but I knew there was little hope because my family could __37__ have that money.
On my birthday my parents told me they had my __38__ outside in the back yard. At once I __39__ out to the yard. There was my bike, __40__ it wasn’t the bike that I thought it would be. This one was pink, old and worn with age. It was so __41__! I thought I __42__ my parents’ feelings because I could see the disappointment __43__ their faces and I was sure they could see it on mine. I __44__ the old bike and rode it, feeling __45__ that I had made my parents feel this way. So I put on a smile, rode as fast as I could and didn’t __46__...
As time went by, I began to understand my parents gave me __47__ much more than just a rusty（生锈的）old bike. They gave me a life lesson about __48__. When you give something out of love, it doesn’t matter what it is in fact. What matters is the love that is in it. I like to remember this __49__ because giving a gift is not about money. It’s about how much love you can feel from it. Do remember, a gift that __50__ two dollars isn’t any less valuable（有价值的）than one that costs one hundred dollars, or even more.

There are so many beautiful cards in the shop that I don't know ________.

1. A.
   which one to choose
2. B.
   to choose which one
3. C.
   which to choose one
4. D.
   to choose on which