Interpret the Level of Statistical Significance for the Event Described

Interpret the level of statistical significance for the event described.
-A study of students taking Statistics 101 was done. 500 students who studied for more than 10 hours averaged a B. 250 students who studied for less than 10 hours averaged a C. This difference was significant at the 0.01 Level. What does this mean?

A) There is not enough information to make any conclusion.
B) The probability that the difference was due to chance alone is greater than 0.01.
C) The improvement was due to the fact that more people studied.
D) There is less than a 0.01 chance that the grades were better by chance alone.