1. The sizes of their necks vary
Infrared has a lower frequency than ultraviolet light.
The answer should be C/Currents
Simple. Air has mass. And if air has mass it also has weight. You can feel air when the wind blows. Or do an experiment. Weigh an empty container. Then pump it to a vacuum. Weigh it again. The difference is the weight of the air inside.
C Time of year I just took the quiz.