Correct Option: A

Almost all the swimming birds have webbed feet which propel them when they are fishing or pursuing a prey into the water. The short legs are situated far towards the lower belly, in order to make easier the swimming action. Flamingos are the exception, gathering both the long legs of the shorebirds and the webbed feet of the ducks. It can feed in deep water and walk easily. Except the Laridae which are more similar to other birds and are able to swim and to walk, all the web-footed birds are very clumsy when they move on the ground. Finally, humans use similar tools when they add flippers to swim faster!