In the middle of a dark forest, there lives an owl(猫头鹰). All the animals know that he is the wisest(聪明的) among all of them. So they often go to him and tell him their troubles. Then the owl always teaches them what they should do.
One day, a little bird goes up to the owl. She is crying. “what's wrong with you?” asks the owl.
“I'm not happy at all. I don't want to be a bird,” the bird says.
“Why don't you want to be a bird?” asks the owl.
“I am so small, weak and useless,” she cries. “I want to be big and strong like the lion. He is very important, but I am not”
Then the owl whispers(耳语) something in her ear. At once the bird dries her tears and goes away. One week later, the bird came back. “Oh, thank you very much. You are a very wise owl,” she says to the owl. “I am very happy now. Every day, I sit on top of the tallest tree and watch for(监视) lions and tigers. When they come near, I shout at the top of my voice. Then my friend all run and hide. They are very thankful to me. I am useful and important now”
The wise owl smiles and says, “No one in this world is useless.”
的中心为顶点，右焦点为焦点的抛物线方程是（ ）