Direction: The question has Statement 1 and Statement 2. Of the four choices given after the statements, choose the one that describes the two statements. Statement 1: Sky wave signals are used for long-distance radio communication. These signals are in general, less stable than ground wave signals. Statement 2: The state of the ionosphere varies from hour to hour, day to day and season to season.

Since ionospheric properties change with time, these signals are in general less stable than ground wave signals. Statement 1 is true because sky waves rely on reflection from the ionosphere for long-distance communication, and this reflection is affected by the ionosphere's variability. Statement 2 is also true; the ionosphere's condition is dynamic and changes based on various factors. Statement 2 is a correct explanation for Statement 1 because the instability of sky waves directly results from the fluctuating nature of the ionosphere.