完形填空

阅读下面短文。从短文后所给的A、B、C三个选项中选出能填入相应空白处的最佳选项。

    Long, long ago, the Elephant had no trunk (象鼻). His nose was 1! But the Elephant's child, just a baby Elephant, was very curious(好奇的) and always asked silly2.

    One morning the curious baby Elephant asked the Kolokolo Bird, "What does the Crocodile3for dinner?" The Kolokolo Bird answered sadly, "Go to the banks of the green river if you want to4 the answer." After a long search, the baby Elephant found the Crocodile by the river bank. "I have been 5 you, Mr Crocodile!" he said excitedly. “Will you please6 me what you eat for dinner?" The Crocodile smiled and said, “Today I will begin with a baby Elephant!" And suddenly the Crocodile7him by the nose. The baby Elephant cried out through his nose. He sat back and began to pull as8 as he could. As he pulled, his nose began to stretch (拉长)! They both pulled and pulled until the baby Elephant was left with a very long nose! All the animals 9his nose. But then he found many ways to10it. He could pick fruits from high treetops, brush away flies, and even breathe when he was underwater!

对于分式 $P=\frac{x}{y}$ ，我们把分式 $P\text{'}=\frac{-y+1}{x+1}$ 叫做 $P$ 的伴随分式. 若分式 $P_1=\frac{a-1}{a}$ ，分式 $P_2$ 是 $P_1$ 的伴随分式，分式 $P_3$ 是 $P_2$ 的伴随分式，分式 $P_4$ 是 $P_3$ 的伴随分式，以此类推…，则分式 $P_{2017}=$ ____.