A). major threat to health; B). remains of prehistoric life; C). in the frog family; D). running and lifting; E). competing for resources; F). warm-blooded; G). objects that have mass; H). graptolites;

Fact 1: Amphibians are the first true tetrapods, or vertebrates with four limbs. Fact 2: All frogs are amphibians. Given the two facts above, the first tetrapods were?
Answer:
C).