Of the Following,which Results Woud NOT Be Indicative of Individual

Of the following,which results woud NOT be indicative of individual differences?

A) Participants from a higher SES household outperformed those from lower SES households on math measures.
B) Participants who had taken a memory enhancing drug for a month outperformed those who had taken a placebo on a working memory task.
C) Male participants tend to outperform femal participants on Raven's matrices on IQ measurement tests.
D) Older adults tend to have more difficulty remembering newly presented information than younger adults.