Bache's Research on Racial Differences in Performance on Reaction Time

Bache's research on racial differences in performance on reaction time tasks found that whites had the slowest reaction times when compared to African Americans or Native Americans. He explained that result by claiming that

A) Native Americans had cheated by anticipating the signals
B) the jobs of African Americans were more akin to the reaction time tasks used
C) whites were not very motivated in the tasks
D) the mind of a white person was more contemplative and less reflexive