Question

a disadvantage of adding a vegetarian hot - food option to a school lunch menu is that it would
force all students to change their diets.
eliminate a meat option from the menu.
help only some students on special diets.
increase the amount of food that is wasted.

Explanation:

Adding a vegetarian option doesn't force diet - change or eliminate meat. Helping some on special diets is an advantage. If students don't like the vegetarian option, it may increase food waste.

Answer:

increase the amount of food that is wasted.