nesting subroutines

例句：

1. 1.The bird is nesting in the tree.
   这只鸟正在树上筑巢。
2. 2. She decided to move back to her hometown after 20 years away.
   她决定在离开20年后搬回故乡。
3. 3.The baby squirrel was nesting in the nest box.
   那只小松鼠正躲在巢穴里。