阅读下面短文, 从短文后各题所给的四个选项（A、B、C、D）中, 选出可以填入空白处的最佳选项。
I was a single parent of four small children, working at a low-paid job. Money was always tight, but we had a 1 over our heads, food on the table, clothes on our backs, and if not a lot, always 2. Not knowing we were poor, my kids just thought I was 3. I've always been glad about that.
It was Christmas time, and although there wasn't 4 for a lot of gifts, we planned to celebrate with a family party. But the big 5 for the kids was the fun of Christmas 6.
They planned weeks ahead of time, asking 7 what they wanted for Christmas. Fortunately, I had saved $120 for 8 to share by all five of us.
The big9 arrived. I gave each kid a twenty-dollar bill and 10 them to look for gifts of about four dollars each. Then everyone scattered(散开). We had two hours to shop; then we would 11 back at the “Santa's Workshop”.
Driving home, everyone was in high Christmas spirits(情绪), 12 my younger daughter, Ginger, who was unusually 13. She had only one small, flat(瘪的) bag with a few candies—fifty-cent candies! I was so angry, but I didn't say anything 14 we got home. I called her into my bedroom and closed the door, 15 to be angry again. This is what she told me.
“I was looking 16 thinking of what to buy, and I 17 to read the little cards in the ‘Giving Trees.' One was for a little girl, four years old, and all she 18 for Christmas was a doll(玩具娃娃). So I took the card off the tree and 19 the doll for her. We have so much and she doesn't have anything.”
I never felt so 20as I did that day.
=4:3:2，则曲线r的离心率等于