The translation of the question is 'What do you have to do to be healthy?'. If you want to answer this question you have to choose the answer that relates to the question. In this case, there is only one answer that talks about healthy food: 'Para estar sano, come cada día una manzana'. The exact translation is: 'To be healthy, eat one apple each day'.
The other answers are really different, one talks about diabetes and the other one about the flu.
