Respuesta :
Answer;
D. indirect observation
Explanation;
-Indirect observation is the method of determining population size in which the population is not aware of the sampler's presence. While using Indirect Observation the members of a population may be small or hard to find. It may be easier to observe their tracks or other signs rather than the organisms themselves.
-This method is least invasive as animals are observed from a distance without interacting with them.
