[单项选择]Most growing plants contain much more water than all other materials combined. C.R. Dames has suggested that it is as proper to term the plant a water structure as to call a house composed mainly of bricks as a brick building. It is certain that all the essential processes of plant growth and development occur in water. The mineral elements from the soil that are usable by the plant must be dissolved in the soil solution before they can be taken into the root. They are carded to all parts of the growing plant and are built into essential plant materials while in a dissolved state. The carbon dioxide (CO₂) from the air may enter the leaf as a gas but is dissolved in the leaf before it is combined with a part of the water to form simple sugars — the base material from which the plant body is mainly built. Actively growing plant parts are generally 75 to 90 percent water. Structural parts of plants, such as woody stems no longer actively growing, may have much less water than g
A. The woody stems contain more wafer than the leaves.
B. Only part of the carbon dioxide in the plants is synthesized.
C. The mineral elements will not be absorbed by the plant unless dissolved in their roots.
D. Air existing around the leaf is found to be saturated.