Which statement best describes the composition of common research animals?

• A. Mice and rats constitute the majority
• B. Primates constitute the majority
• C. Zebrafish constitute the majority
• D. Dogs and cats constitute the majority

Answer: (A)

The main idea is that small rodents, especially mice and rats, make up the largest share of animals used in most research settings. They’re favored because they’re relatively inexpensive to obtain and maintain, reproduce quickly, and have extensive existing bred strains and genetic tools that support a wide range of studies. This practicality means they dominate the animal population in typical laboratories, so the statement that mice and rats constitute the majority best reflects how common research animals are organized in many facilities. While primates, dogs and cats, and zebrafish are important models and used in many areas, they are much less numerous overall compared to mice and rats.