Select the correct answer.
what is responsible for the difference between the time the moon takes to go through a complete set of phases and the time it takes to
complete one complete revolution of the earth?
a.
the movement of the earth along its orbit
b.
the changing speed of the earth's rotation
c.
the synchronous rotation of the mood
d.
the tilt of the earth about its axis

A. The movement of the Earth along its orbit  

Explanation:

The moon orbits the Earth once every 27.3 days. This is the sidereal month. It is measured against the background stars.

However, the Earth is also orbiting the Sun, and the moon needs extra time to catch up to its previous position relative to the Sun. This is the synodic month. It takes 29.5 days.

B is wrong. The rotational speed of the Earth constant. It makes one revolution every 23 h 56 min 4.09053 s.

C is wrong. The synchronous rotation of the moon does not affect its orbital speed.

D is wrong. The tilt of the Earth's axis affects only the moon's angle in the sky.