The Star Algol in the Constellation Perseus Has These Unusual

Multiple Choice

The star Algol in the constellation Perseus has these unusual characteristics. Every 68.75 hours its brightness dims suddenly from apparent magnitude 2.3 to apparent magnitude 3.5 and remains there for a few hours before returning just as suddenly to 2.3. In addition, halfway through this 68.75-hour period, the apparent magnitude becomes slightly dimmer than 2.3 for a few hours and then returns to 2.3. From this information alone it is possible to classify Algol as a(n)

A) optical double.
B) eclipsing binary.
C) totally eclipsing binary.
D) partially eclipsing binary.