It, its, itself, they, their or themselves?

Điền vào chỗ trống it, its, itself, they, their hoặc themselves để hoàn thành đoạn văn dưới đây.

The entire wing of a bat is called the patagium. Many species also have a membrane between their hind limbs enclosing the tail.The patagium is full of fine blood vessels, muscle fibres and nerves. When it is cold, these bats wrap  up in  wings like a coat. In warm weather  flap  wings in order to cool  bodies.

The bat has claws on  thumbs and sometimes on the toes of  fore and hind limbs. The rear claws enable  to hang  on to a tree branch or ledge.

All bats are active at night or at twilight, so  eyes are poorly developed.