ADBECF
Mainstream research. Sentence D then takes it a step forward and mentions a research person who talks about how she first used it 13 years ago. The rest of the sentences are quotes made by her and are easier to understand in terms of the sequence. Sentence B then talks about her approach and sentence E is a comment on how this was perceived at the time. Sentence C is a reflective comment on how the times have changed with the last sentence F describing specific instances of the same. This makes choice (d) correct.