6. what common unit of time is related to this lunar motion?

Time is measured in Lunar month

Explanation:

The lunar month is the time the moon takes to pass through each phase i.e new moon to half and then to the full moon etc.  Taking about 29 days, 12 hours, 44 minutes and 3 seconds to complete this rotation on its axis. Thus the moon only takes 27.3 days to complete this action. Thus as the moon goes back in its orbit it takes 2.2 days to catch up. Moon also has the same elliptical longitude as that of the sun as seen from the earth's surface. The motion of the moon is in an eastward direction along with the motion of stars, thus it shows the same face to earth every day. This is evident as it moves just 13 degrees in 24 hours.

It’s either c or d as the answer.