If Our Circadian Clocks Are Not Reset Each Morning by Exposure

If our circadian clocks are not reset each morning by exposure to light, they:

A) tend to run a cycle that is a little shorter than 24 hours.
B) tend to run a cycle that is a little longer than 24 hours.
C) tend to run on a 12-hour cycle.
D) still run exactly on a 24-hour cycle.