Explanation:

Introduction:
The question asks for the animal that hangs upside down on a tree. We need to identify the correct animal among the given options.

Analysis of Options:
Let's analyze each option to determine which one matches the given criteria.

1. Parrot: Parrots are known for their ability to fly and perch on trees. However, they do not hang upside down on trees. Therefore, option 'a' is incorrect.

2. Eagle: Eagles are large birds of prey known for their strong flight and hunting skills. They typically build nests on tall trees or cliffs, but they do not hang upside down on trees. Therefore, option 'b' is incorrect.

3. Bat: Bats are the only mammals capable of sustained flight. They have a unique ability to hang upside down from tree branches or caves for roosting and sleeping. This characteristic makes them the correct answer to the question. Therefore, option 'c' is correct.

4. Sparrow: Sparrows are small birds that are capable of flying and perching on trees. However, they do not hang upside down on trees. Therefore, option 'd' is incorrect.

Conclusion:
Among the given options, the animal that hangs upside down on a tree is a bat (option 'c'). Bats have the unique ability to roost and sleep in an inverted position, which sets them apart from the other animals mentioned.