C because he is making a hypothesis that coloration which is the independent variable is making the change.
The first option is correct.
Earth always has two surrounding gravitational forces, one proceeding from the moon and one from the sun.
The sun's pull, despite the fact our sun is further then the moon, is stronger and creates the high tide, and the moon the low tide. But as we know our earth moves, now exposing the other side to the sun which in turn leaves the other side of earth with the high tides and the other with the low tides. Tides never move, what moves is earth.
Hope it helped,
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What happens is the plants absorb the carbon dioxide in the air which we produce by breathing in oxygen and breathing out carbon dioxide. They then combine the carbon dioxide, water, and sunlight because most plants cannot live with sunlight, to create glucose which is the second formula you have in your question.
