The correct answer is: D. Dipper shovel.
A dipper shovel is a type of excavator that is most suitable for digging under water. It has a long arm with a bucket at the end, which is used to scoop up dirt and debris. The bucket is then lifted out of the water and emptied onto the ground.
Drag lines, hoes, and clam shells are all types of excavators that can be used for digging under water, but they are not as well-suited for this task as dipper shovels. Drag lines have a long cable that is used to drag a bucket through the water. Hoes have a short arm with a bucket at the end, which is used to push dirt and debris around. Clam shells have two hinged jaws that are used to open and close like a clam.
Dipper shovels are the best type of excavator for digging under water because they have a long arm that can reach deep into the water, and they have a bucket that is large enough to hold a lot of dirt and debris.