To effectively take carbon out of the atmosphere, the correct options from your list are:
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Limestone formation: This process involves carbon dioxide reacting with calcium ions in water to form calcium carbonate, which can reduce atmospheric CO2 over geological timescales.
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Photosynthesis: Plants absorb carbon dioxide from the atmosphere during photosynthesis, converting it into organic matter and releasing oxygen.
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Equilibrium with the ocean: Oceans absorb a significant amount of carbon dioxide from the atmosphere, which can contribute to decreasing its concentration.
The other options:
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Burning fossil fuels: This releases carbon dioxide into the atmosphere, increasing carbon levels.
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Respiration: This process releases carbon dioxide into the atmosphere as organisms break down food for energy.
So, the correct answers for taking carbon out of the atmosphere are limestone formation, photosynthesis, and equilibrium with the ocean.