Correct Response: C. While resistance exercises and proper diet can contribute to increasing muscle strength and size, the hormone testosterone is required for significant growth in muscle mass. Females have lower rates of testosterone production than males, and so do not generally develop large muscle mass, even while they effectively train to increase muscle strength (B), endurance, and tone. This is true, whether or not a female begins training with well-toned muscles (A), or focuses on the lower body (D).