Which best describes the role of resistance training in a healthy weight-gain program for an underweight person?

Resistance training helps build lean muscle so weight gained includes a higher proportion of muscle rather than fat when combined with a caloric surplus.

Only aerobic training should be used during weight gain because it exclusively promotes muscle hypertrophy when paired with extra calories.

Resistance training is unnecessary because all weight gain will be lean if the person consumes enough calories regardless of physical activity.

Resistance training always prevents any fat gain, so calorie distribution and food choices are irrelevant when exercising.