What is the most likely reason that stickleback populations in certain lakes have less armor than their ocean-dwelling relatives?

The lakes have higher water temperatures which makes growing armor difficult.

The primary predators in the lakes are different, making heavy armor less advantageous.

Sticklebacks in lakes have a different diet that lacks the minerals needed to form armor plates.

Random genetic mutations caused all the lake sticklebacks to lose their armor simultaneously.

A trait is considered "adaptive" in an evolutionary context when it:

is the most complex trait an organism possesses.

is a trait that appears in every individual of a species.

changes randomly from one generation to the next.

increases an organism's likelihood of surviving and successfully reproducing in its specific environment.

A decrease in body size to be less visible.

The development of brighter coloration for mating.

An increase in the average amount of armor plating.

A shift to a diet of different aquatic plants.