All the Following Statements Are True

All the following statements are true.Which one explains why mean solar time differs from apparent solar time?

A) The length of a solar day is not always exactly 24 hours.
B) Earth's rotation period is actually about 23 hours and 56 minutes,not 24 hours.
C) Earth's axis precesses with a period of about 26,000 years.
D) The Sun reaches the meridian at different times at different longitudes within the same time zone.