Ellen Wants to See If the Level of Lighting in a Room

Ellen wants to see if the level of lighting in a room will affect the performance of individuals on an IQ test. She lets one group in her study have very bright lights and a second group have more normal lighting. She finds that the individuals in the bright light group have better scores on the test than do the individuals in the normal light group. The difference between the two groups' scores is statistically significant, which means

A) lighting definitely makes a difference.
B) the difference between the groups is due to chance.
C) lighting significantly affects performance.
D) the difference between the groups is probably not due to chance.