Question 7 of 10 multiple choice: select the best answer and click "submit." many ocean creatures make their shells out of calcium carbonate (caco3). this process is more difficult when the ocean ph is lower. why would greenhouse gas emissions harm these creatures? a. the concentration of salt in the water has decreased. b. calcium carbonate is a major greenhouse gas. c. the polar ice caps are made of freshwater. d. co2 acts as an acid when absorbed by the ocean.