Which Experience of "Trial and Error" Helped Mary Waters Develop

Which experience of "trial and error" helped Mary Waters develop stronger interview questions regarding West Indian immigrant experiences?

A) conducting an interview without an interview schedule,and then developing a schedule for the next interview
B) asking questions that did not elicit strong responses,and then rewording the questions for more effective responses
C) seeking interviewees through purposive sampling,and then switching to snowball sampling
D) starting an interview as an oral history,but then shifting it to a life history approach that is more scientific and generalizable