Positive energy balance is important when
a. weight stability is desired.
b. a child is growing.
c. you're stressed.
d. weight loss is desired

The answer to this question is "A" because it shows that you are happy with your weight

Positive energy balance is needed when a child is growing.  Growth requires extra calories and proteins.  Hence the term positive meaning additional.
You want equal energy balance not to gain weight because positive energy balance means having more calories than you need.

True your body needs vitamins such as protein, vitamin d, fish oil etc