The Light Intensity from a Particular Star Remains Essentially Constant

Multiple Choice

The light intensity from a particular star remains essentially constant except for short and regular decreases, after which it increases again to its constant value. What is the MOST plausible explanation for this phenomenon?

A) One star is regularly eclipsing its companion as they move in mutual orbits when the plane of those orbits is close to Earth's line of sight.
B) A variable star is pulsating in size, temperature, and intensity.
C) The star is undergoing periodic supernova events.
D) Shells of absorbing gas and dust are being periodically ejected from the star's surface and are subsequently dispersing into space.