Consider the question. These belong to the class of creature that were the first true tetrapods:
Options:
- (A) millipede
- (B) crabs
- (C) four limbs
- (D) bullfrogs
- (E) gastropod
- (F) a fish
- (G) warm-blooded
- (H) insects
 What is the step-by-step reasoning process to arrive at the answer: (D)?
Amphibians are the first true tetrapods, or vertebrates with four limbs. Bullfrogs eat other amphibians. Bullfrogs are of the class of creatures that were the first true tetrapods.