a, because exercise doesn't just aid the prevention of certain diseases, it helps prevent many diseases. i would've chosen d if it wasn't so specific but a is the correct answer.
Minerals <em>maintain water balance </em>
Carbohydrates <em>provide basic energy</em>
Proteins <em>repair body tissue</em>
Fats <em>maintain body temperature</em>
Vitamins <em>absorb other nutrients</em>
Hope that helps!