A Popular Brand of AAA Batteries Has an Effective Use

A popular brand of AAA batteries has an effective use time of 12.3 hours, on average. A startup company claims that their AAA batteries last longer. The startup company tested 24,000 of their new batteries and computed a mean effective use time of 12.32 hours. Although the difference is quite small (72 seconds-or just over a minute) , the effect was statistically significant (P-value < 0.0001) .
The most likely explanation for a 72-second difference being reported as statistically significant is

A) that old designs typically have more variability than new designs.
B) that 72 seconds is actually a substantial time difference for battery life.
C) that the sample size is very large, so even slight differences seem significant.
D) All of the answer choices are very likely explanations.