Needed for most chemical reactions and makes up of 70% of cells.
a. water
b. air
c. food
d. living space
e. carbohydrates

A is the answer because we our body is almost made of water

C.water water is the most important,There are tens of thousands of different types of chemical reactions and interactions going on everywhere in the body all the time. Every one of these  requires water to be present.

And a) oxygen i believe