Which of the following is an example of cooperation among organisms?
A.
Army ants link themselves together to form a "bridge" so that their colony can cross a stream.
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.
A fly gets caught in a spider's web but escapes before being eaten.