阅读下列短文，从每题所给的四个选项（A，B, C和D）中，选出最佳选项。
Happiness depends upon ourselves
I stared at the word "Happiness", my creative-writing assignment (作业) about emotion, on my blank(空白的) paper. No format(格式) at all.
It was not the lack of structure (结构） 1the word "happiness" that was 2 me. Anything else I could have 3 well, say, jealousy (嫉妒) or pain. But I was 4 to write about happiness.
There was a 5 at my bedroom door. "Hey, Sarah?" asked a small voice. "Can I come in?" "Rachie." I said to my five-year-old sister. "I'm 6 now."
"But this is important."
I 7. "Okay, then." Rachie came in. "Um, I caught my favourite butterfly. It's 8 pretty. But I let it go because Mommy said it would die." "So, what's the 9?" I asked. "Well," she whispered 10 she were about to share a deep 11. "When I set it free, I was 12. Does that make me a mean person?" I 13. "Of course not. You were just happy it was free." I gave her a 14. "Now I have work to do." "What work?" she asked. I 15 my blank paper. "I have to write about happiness." "Oh, that's easy." "What's your happiness?" I asked. She thought a few seconds. "Butterflies," she said 16 and left.
Butterflies! I thought about our 17. She was happy to catch the butterfly and happy to see it go. Maybe she was right. Butterflies 18 nothing but happiness. Maybe butterflies aren't exactly the 19 to happiness, but there is something to be said about the simple things in 20. And with that, I started to write.
