Final answer:
The ethnographic fieldwork is the main research method used in 'Gang Leader for a Day,' which involves deeply immersing in a community to understand how individuals view their social roles. The correct option is A.
Step-by-step explanation:
The main research method used as the basis for Gang Leader for a Day is a. Ethnographic fieldwork. This approach involves the immersion of the researcher in the natural setting of a social community to observe and experience their everyday life and culture. The essence of an ethnographic study is to understand how the subjects perceive their own social standing and how they identify themselves within their social group.
Sudhir Venkatesh, the author of 'Gang Leader for a Day,' conducted his research by spending extensive amounts of time within the community he was studying, becoming an active participant in their daily affairs to gain a deeper insight into their lives.