Fact 1: Birds are endothermic tetrapod vertebrates. Fact 2: Legs define Tetrapods. Given the two facts above, birds are vertebrate endotherms with what?
Options:
i. fat;
ii. Energy;
iii. legs;
iv. like some sharks;
v. Tail;
vi. invertebrates;
vii. arms;
viii. four;
Answer:
iii.