When two or more organisms cooperate, they work together toward a goal which benefits all of the cooperating organisms. Cooperation can occur between organisms of different species or organisms within the same species.

Which of the following is an example of cooperation among organisms?

A. A fly gets caught in a spider's web but escapes before being eaten.

B. A flatworm attaches itself to the gills of a crab to obtain bits of the crab's food.

C. Two cows graze upon the same pasture.

D. Army ants link themselves together to form a "bridge" so that their colony can cross a stream.