In the Statistical Calculations for This Experiment, the Standard Deviation

In the statistical calculations for this experiment, the standard deviation in the fixed-interval reaction time experiment is usually lower than that of the random-interval reaction time experiment.  What does this mean?

A) It means that average random-interval reaction times are typically shorter than average fixed-interval reaction times.
B) It means that there is less variability in the data for the fixed interval reaction time trials than in random-interval trials.
C) It means that average random-interval reaction times are typically longer than average fixed-interval reaction times.
D) It means that there is more variability in the data for the fixed interval reaction time trials than in random-interval trials.
E) It does not indicate any particular trend for fixed-interval vs. random-interval reaction time trials.