Final answer:
The best population to be estimated by an area-based survey is flowers in a field using a quadrat to count the number of individuals which allows for estimates of population size and density. Option a is correct.
Step-by-step explanation:
The population best estimated by an area-based survey is flowers in a field. This method is specifically tailored for immobile organisms, which include plants. An area-based survey involves using a quadrat, a square structure that is randomly located on the ground to count the number of individuals within its boundaries.
With mobile organisms, such as rodents, fish, and birds, scientists would typically use mark and recapture techniques to estimate population sizes because these organisms can move out of a given area before they can be counted.
Quadrats are advantageous because multiple samples can be taken at random locations within the habitat to estimate overall population size and density.