Because of its simplicity and measurement consistency across populations, is the most widely used measure to determine overweight and obesity.

BMI

Explanation:

Body Mass Index or BMI is a unit that widely used to determine the nutritional status of someone. You can find BMI by dividing the body mass with the square of height. This measurement is more accurate than the mass alone since it uses height. But this measurement is not good for an athlete since they have more muscle mass. Their BMI will be higher and make them seems overweight but the excess comes from the muscle mass, not the fat.

the first question's answer is a.