Question

select the correct answer from each drop - down menu. complete the passage about cyanobacteria. about three billion years ago, single - celled organisms called cyanobacteria lived in earth’s oceans. they thrived on the ocean’s abundance of
, which they used during the process of photosynthesis. much later, this process allowed organisms, such as fish, to survive by extracting dissolved
from ocean waters.

Explanation:

For the first drop - down: Cyanobacteria perform photosynthesis. The reactants of photosynthesis include carbon dioxide ($\ce{CO_2}$). So the first blank should be filled with a substance like carbon dioxide (assuming common options in the drop - down related to photosynthesis reactants, e.g., carbon dioxide). For the second drop - down: The product of photosynthesis by cyanobacteria is oxygen ($\ce{O_2}$), which dissolves in water. Fish and other aquatic organisms extract dissolved oxygen from water to survive. So the second blank should be filled with oxygen.

Answer:

First drop - down (example, depending on options): carbon dioxide (or relevant option like $\ce{CO_2}$ - related option in drop - down)
Second drop - down (example, depending on options): oxygen (or relevant option like $\ce{O_2}$ - related option in drop - down)

(Note: Since the actual drop - down options are not provided, the above is a general explanation based on biological knowledge of photosynthesis and aquatic respiration. If the drop - down options had specific choices like "carbon dioxide", "glucose", "oxygen", "nitrogen" etc., the first would be carbon dioxide and the second would be oxygen.)