In theory, to gain one pound of body weight per week, you d need to consume an additional:

Aten grams of fat per meal.
Bsix servings of protein per week.
C500 calories per day.
D1000 calories per day.

Verified Answer :

In theory, to gain a pound of body weight per
week, one must consume an additional 1,000 calories per day. An approximate
3,500 calories is equivalent to a pound of body weight. If a person
continuously consumes more than 3,500 calories over a period of time it is
expected that this person will gain 1 pound of weight. 

Nutritionists
usually suggest that an
underweight person should add between 500-1,000 calories per day to encourage a
1-2 pound increase in body weight. Because being underweight sacrifices one's
immunity and overall health.

The answer is C. 500 additional calories per day.