Prop roots are the modified aerial adventitious roots of corn that

a) enable the root system to obtain oxygen
b) support tall, top-heavy plants
c) enable the root system to anchor
d) wrap around other plants to support tall, top-heavy plants

Prop roots are the modified aerial adventitious roots of corn that enable the root system to anchor.

Explanation:

Prop roots are the last roots to develop. They appear when the corn plant presents at least ten real leaves, originating from the first two aerial knots and directing to the ground.  These are thick, pulpy, and vigorous, and penetrate the ground up to 15 cm deep. Their principal function is to support, giving the plant a better anchor. They can also participate in water and nutrients absorption, but this is not their primary function.

the dark variety, as they are not visible on the dark tree barks

explanation: