He most useful advantage of adding a vegetarian hot-food option to a school lunch menu is limiting the amount of food that is wasted by the school. Presenting an additional choice for teachers and staff. Providing an additional choice for students on restricted diets. Reducing the cost of lunch options for students and teachers.

The correct answer is: "Providing an additional choice for students on restricted diets"

It actually introduces a new and different option for everybody, but it specially will satisfy the needs of those who are restricted in terms of menu by a vegetarian lifestyle.

This does not mean that the cost of this new vegetarian option is lower, or that it involves that less food is wasted.