Question

Thick bark helps a tree survive when

a. the rain washes away the soil
b. the weather is colder than normal
c. there are storms with strong winds
d. the is little sunlight avaliable

I think it is b

If you don't know what the right answer is in a multiple choice question, try to eliminate the other alternatives.

a. Bark is not in the soil.
c. Winds can blow a tree down regardless of the thickness of the bark.
d. The leaves contain the chlorophyll that takes advantage of the sunlight.

I guess that "leaves" b. You are right.