Technician exam question T3C09

WhyThe best time for long-distance 10-meter band propagation via the F region is generally from dawn to shortly after sunset during periods of high sunspot activity. The F region, the ionosphere's highest and most persistent layer, is most strongly ionized by direct sunlight and during periods of high sunspot activity carries enough ionization to reflect 10-meter signals well, so the best 10-meter DX window is daytime hours, from dawn to shortly after sunset, during those high-sunspot periods, answer A. The nighttime windows in B and D don't match when the F region is most active on 10 meters, and low sunspot activity (C) simply doesn't provide enough ionization for reliable 10-meter F region propagation regardless of time of day.