Unicellular organisms excrete waste by a contractile vacuole. A vacuole is membrane-enveloped organelle in a cell that is found in lots of microorganism. It expands, filling with water then contracts, removing all of its contents to the exterior of the cell.
Probably very distantly, but sharks are fish, and dolphins are mammals.
Answer:
option 3 in 1st one and option 4 in 2nd one I think
D i believe, i could be wrong though
