On which of the following amateur bands is long-path propagation most frequent?

Long-path propagation occurs when a radio signal travels the longer way around the Earth to reach the receiving station, typically along the twilight zone or 'gray line.' The 20-meter and 40-meter bands are particularly well-suited for this because they offer a consistent balance of low D-layer absorption and reliable F-layer refraction during these transitional daylight/darkness periods. Higher frequency bands like 10 or 6 meters often lack the required Maximum Usable Frequency (MUF) over the entire long path, while lower bands like 160 or 80 meters suffer from too much absorption if any part of the path is in daylight. Thus, 20 and 40 meters provide the optimal 'sweet spot' for long-path DXing.