Because they were omnivores and because they were capable of adapting quickly to changing food and environments, _________ moved into the niches left by reptiles - particularly dinosaurs. A. Amphibians B. Birds C. Mammals

The answer is C. Mammals.

Step 1: Understand the question. The question is asking which group of animals moved into the niches left by reptiles, particularly dinosaurs, because they were omnivores and could adapt quickly to changing food and environments.

Step 2: Analyze the options. The options given are A. Amphibians, B. Birds, and C. Mammals.

Step 3: Recall relevant information. Mammals are known for their adaptability and many are omnivores, meaning they eat both plants and meat.

Step 4: Apply the information. Given the information in the question and what we know about mammals, we can conclude that mammals are the group of animals that moved into the niches left by reptiles.

So, the answer is C. Mammals.