Answer
Ocean acidification due to dissolved carbon dioxide and placement of $C_{3}$ and $C_{4}$ plants both revolve around atmospheric carbon dioxide concentrations, which have been rising steadily. More carbon dioxide shifts where acid-sensitive organisms like many corals can live and where $C_{4}$ plants, with their carbon-dioxide concentrating mechanisms, will be at an advantage.
Work Step by Step
This question asks you to see connections among several things: global atmospheric carbon dioxide concentrations, ocean pH, marine organism placement, and where different kinds of plants (defined biochemically) live. It should highlight just how complex biology is and how many subjects it touches at one time.
