A Statement You Will Sometimes Hear People Say Is That

A statement you will sometimes hear people say is that a day is not 24 hours but is really 23 hr. 56 min. and 4 sec. What does this refer to?

A) This is sidereal time, not solar time; a solar day is 24 hours.
B) The original definition of the hour was off, and with more accurate atomic clocks we now realize the real day is this length.
C) It is just an urban myth; the day really is 24 hours long.
D) Our clocks drift that much each day, and we average out the affect with period time shifts, like leap years and leap seconds.