Answer:
d. naturalistic observation
Explanation:
Naturalistic observation -
It is the method of observation in the research field , where the method used is observing the object of study in their particular natural environment , is referred to as naturalistic observation.
This helps to get a pure and proper source of knowledge for the research work , and helps to understand the subject is the best possible way.
Hence , from the given information of the question,
The correct option is d. naturalistic observation .