Animals That Swim Expend Less Energy to Move Than Do

Animals that swim expend less energy to move than do animals that walk or fly because

A) water provides less resistance than air.
B) gravity has more impact on aquatic animals than it does on terrestrial animals.
C) aquatic animals do not have to use muscles to move their fins and tails.
D) the streamlined shape and nonstick surfaces of aquatic animals reduce resistance due to drag.