Most dissolved carbon in the ocean is used to form which structure in marine organisms?
the fronds of giant algae
the muscle tissue of small fish
the nerves of giant mollusks
the skeletons of coral polyps

D

Explanation:

Photosynthesis by tiny marine plants (phytoplankton) in the sunlit surface waters turns the carbon into organic matter. Many organisms use carbon to make calcium carbonate, a building material of shells and skeletons

The skeletons of coral polyps.

Explanation:

The photosynthesis by the aquatic plants, atmospheric carbon dioxide dissolved in the oceanic water, the decomposed and degraded matter of animals and plants can increase the concentration of the carbon dioxide in the oceanic water. This carbon dioxide can be useful to develop the coral reef the hard skeleton structure composed of calcium carbonate by the colonies of the coral polyps.  

the answer is: they occur when the sun, moon, and earth are aligned. in spite of their name, these tides occur twice a year in the spring and fall.

the answer is trees if i'm not mistaken