I believe that the answer would be D., Water.
Water gives you alot of energy, believe it or not. If you
were not to drink water for days, you will feel very lazy
and down.
Hope this helps!
Cardiovascular is probably your answer
Cardio- the heart
Vascular- vessels
Circulatory- blood
Just go look on some of the questions on Bradley I'm sure you'll find the answer there
Carbohydrates, Lipids and proteins