Matthew is completing his master's thesis, which addresses the culture of outlaw motorcycle gangs. for the past six months, he has been riding with a gang, observing and describing behaviors in an attempt to present a view of these groups from a gang member's perspective. like mario brajuha, he is determined to keep the identities of his subjects confidential. which research method is matthew employing? a. case study b. documentary c. unobtrusive measures d. participant observation