Variations in the Luminosity of Quasars Over the Span of a Few

Variations in the luminosity of quasars over the span of a few hours are an indication

A) of the rapid rotation of the sources.
B) that these objects are actually binary systems in which one sees mutual eclipses.
C) of the relatively small size of the emitting regions.
D) of obscuring gas and dust clouds moving in front of them from Earth's point of view.