The essential function of photosynthesis in terms of plant needs is ______.

A．The mineral elements will not be absorbed by the plant unless they are dissolved in its root.
B．The woody stems contain more water than the leaves.
C．Air existing around the leaf is found to be saturated.
D．Only part of the carbon dioxide in the plant is synthesized.

A．a plant efficiently utilizes most of the water it absorbs
B．carbon dioxide is the essential substance needed for plant development
C．a plant needs more water than is found in its composition
D．the stronger the wind, the more the water vapor loss