I believe that the question has options, and that those are the options:
1) age and gender.
2) birth order and genetic endowments.
3) educational level and control of income.
4) Each of these could contribute to the amount of food available to family members.
The correct answer is the last option: Each of these could contribute to the amount of food available to family members.
For example, in some cultures men and older children get to eat more, and also higher education allows for being able to afford buying more food.
