Maintaining a healthy lifestyle through diet and exercise is important, but it has no effect on the immune system. but it actually decreases the immune system. and it has been scientifically proven to boost the immune system. but it has not been proven to boost the immune system.

D). But it has not been proven to boost the immune system.

Explanation:

As per the question, maintaining a healthy lifestyle through diet and exercise is significant however it has not been proven to boost the immune system. A healthy lifestyle including a balanced diet along with regular exercise corresponds to enhancing immunity and contracts the risk of diseases yet no specific proof has been scientifically approved that a healthy lifestyle(including exercise and healthy diet) nurtures the immune system. Thus, option D is the correct answer.

what are the answers?

that is based on your opinion not an answer someone can just give you unless you want to lie on your opinion. no offense wasn't trying to be rude. tip: use words like instead of don't put do not and you get what i mean