Answer:
B. A Bristlecone pine forest that contains trees that are over 500 years old
Step-by-step explanation:
An old growth forest is forest that has been left to grow undisturbed for a very long time such that it has attained a relatively stable climax community. Old growth forests are sometimes referred to as primary, virgin or late seral forests.
Option C and D are incorrect. Both clearly negate the definition of an old growth forest. Option A cannot be correct because it indicates a short term growth.
The correct option is B. 500 years a long time that is enough for an undisturbed forest to reach a climax stage.