Phytoplankton are single-celled, photosynthetic organisms living at the surface of the ocean. How do phytoplankton affect the Earth's carbon and oxygen cycles when they perform photosynthesis?
A. They add both carbon dioxide and oxygen to the atmosphere.
B. They add oxygen to and remove carbon dioxide from the atmosphere.
C. They remove both carbon dioxide and oxygen from the atmosphere.
D. They add carbon dioxide to and remove oxygen from the atmosphere.