The correct answer is option 2: Bat. Bats are the only mammals that can fly. They have the unique ability to sustain flight, thanks to their specialized wings and the fact that they are lightweight. Bats are nocturnal creatures and use their wings to navigate and hunt for insects in the dark. Despite being mammals, bats have adapted to a flying lifestyle, allowing them to access different habitats and food sources. It is important to note that although some other animals, such as flying squirrels, can glide through the air, they cannot truly fly like bats. So, when considering mammals, bats hold the distinction of being the only ones capable of sustained flight.