Which of the following bands may provide long-distance communications via the ionosphere’s F region during the peak of the sunspot cycle?

During the peak of the 11-year sunspot cycle, the sun emits exceptionally high levels of ultraviolet radiation. This intensely ionizes the F region of the ionosphere, raising the maximum usable frequency (MUF) high enough to reflect signals that would normally pierce right through into space. The 10-meter (28 MHz) and 6-meter (50 MHz) bands are perfectly positioned to take advantage of this heightened solar activity. When the MUF rises above 50 MHz, global communications on the 6-meter 'magic band' become possible using standard F-layer skip. The other choices (23 cm, 70 cm, and 1.25 m) are UHF and high VHF frequencies. Their wavelengths are far too short and their frequencies too high to ever bounce off the F region, even during the most intense solar maximums; they will simply pass straight through the ionosphere.