路的一边是田野，葱葱绿绿的，非常可爱，像一片柔软的绿毯。

请根据对话选词填空

   ducks    quiet     nature park    people   buildings

    There is a____. The nature park is____. There aren't many ____. There aren't many tall____. There are some animals. They are____and rabbits.

设双曲线$\frac{x^2}{4}$﹣y²=1的右焦点为F，点P₁、P₂、…、P_n是其右上方一段（2≤x≤2$\sqrt{5}$，y≥0）上的点，线段|P_kF|的长度为a_k，（k=1，2，3，…，n）．若数列{a_n}成等差数列且公差d∈（$\frac{1}{5}$，$\frac{\sqrt{5}}{5}$），则n最大取值为____