Final answer:
The correct option is b. area-based. The Christmas bird count conducted by the Audubon Society is an example of an area-based survey where volunteers count the number of bird species within a 24-kilometer circle using mark and recapture method.
Step-by-step explanation:
The annual Christmas bird count conducted by the Audubon Society is an example of an area-based survey. During this survey, volunteers count the number of individuals of every bird species they can see or hear within a 24-kilometer circle. The survey method involves sampling a representative portion of each habitat to make inferences about the population as a whole.
For immobile organisms such as plants or for very small and slow-moving organisms, a technique called mark and recapture can be used. This method involves marking a sample of captured animals and then releasing them back into the environment to mix with the rest of the population.