Why is it a good idea to study experimental subjects in their natural enviroment?

So you know your envoirment so you know what not to destroy and what to keep safe because that's what you live in so you wanna know about the environment

A. so that the experiment is cheaper and easier to conduct

b. so that a specific problem can be solved as quickly as possible

c. so that no one else will know what is being studied

d. so that they respond to the test as they would normal conditions