C4 and cam plants are
a.
adaptations to arid environments
b.
adaptations to moist environments
c.
more common than c3 plants
d.
less efficient at water conservation than c3 plants

B. Adaptation to moist environments.

Explanation:

Plants are categorized by their process of photosynthesis, they are divided into C3, C4, and CAM.

C3 are the most common plants in the world.

C4 plants are found in grasslands, tropics, subtropics, and warm temperate zones. The photosynthesis process is a biochemical modification of the C3 plants.

Finally, CAM plants are adapted to low water regions like arid environments, the most common example of a CAM plant is a cactus.

As we can notice about the descriptions given C4 and CAM plants are adaptations to moist environments because they could be in arid zones with low water or in tropic zones.

I hope this answer helps you.

this is math not biology xd