Prescribed burns are used to a. clear out undergrowth b. prevent larger forest fires c. manage forests d. all of the above

D) All Of The Above 
I think this is right.

Actually, all of the above. Firefighters have used fires to COMBAT forest fires, as the controlled fire they set will suck out all the oxygen, which is what bigger fires need in order to continue, and if they can't get it, they'll decrease in size. Also, the heat and wind motion from the fire can combat that of the larger fire, if they do it correctly.

You can use prescribed burns to also control and manage forests and to clear out any undergrowth.

Answer is d: All of the above

~Hope this helps!