Answer: I'LL GO WITH "B".
Explanation: HUNGER IS THE GREATEST STRUGGLE MANKIND WILL EVER FACE.
Let´s face this as deep as we can. Yes, indeed. The biggest problem and reflect of "The glass of milk" is the lack of having something to eat. But in a deeply context it focus on the fact that our biggest problem will always be the lack of something, the necessity of something beyond our power.
Love, food, peace, calm, a planet where we can live, water,shelter.