|Scientist reported last month on a sign of relative solar _____; the solar wind, a rush of charged particles continually spewed from the Sun at a million miles an hour, had diminished to its lowest level in 50 years.
Answer is AD. In this sentence it says " had diminished", I think past perfect means anything happened before a past point which means before scientist reported. So I think before scientist reported it diminished and after reported should be increased or unstable , so should choose BF. So can anyone tell me why choose AD please?