The main characteristic of a carbon sink is that
a. it emits no carbon
b. it absorbs no carbon
c. it emits more carbon than it absorbs
d. it absorbs more carbon than it emits

The correct answer is D. It absorbs more carbon than it emits. It is basically like a giant storage or a giant container for carbon that is used to remove excess CO2 from air. The process which is called carbon sequestration is very useful in preventing things like global warming and the greenhouse gasses effect. The less carbon it emits the better.