How does the ionosphere affect radio waves with frequencies below the MUF and above the LUF?
They are refracted back to Earth✓Bonne réponse
They pass through the ionosphere
They are amplified by interaction with the ionosphere
They are refracted and trapped in the ionosphere to circle Earth
Explication
Between the LUF and the MUF the wave is bent gradually as it enters the increasing electron density of the ionosphere until its path curves back toward the ground. Below the LUF absorption removes it, above the MUF the bending is insufficient and it escapes into space.