Is all the options increase, which ones would serve to remove CO2 from the atmosphere?

A. Photosynthesis

Explanation:

Photosynthesis is a process in plants produce food materials by absorbing carbondioxide from the atmosphere which decreases the concentration of carbondioxide in the atmosphere. In photosynthesis reaction, plant take water from the soil and carbondioxide from the atmosphere in the presence of sunlight produces glucose and oxygen. Glucose is stored in different parts of plant such as grains, stem and roots while oxygen is released in the atmosphere.

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.