The absorption of human-generated CO₂ by the oceans __________.

• A. increases the oceanic concentration of carbonic acid
• B. increases the oceans' acidity and pH
• C. reduces the carbonate ion concentration in the oceans and threatens calcifying organisms in marine ecosystems
• D. increases the hydrogen ion concentration in the oceans but decreases the carbonate ion concentration and threatens the livability of the oceans for organisms that produce calcium carbonate shells