If a Repeated-Measures Study Shows a Significant Difference Between Two

If a repeated-measures study shows a significant difference between two treatments with α = .01,then you can assume that ____.​

A) ​the value of Cohen's d is large
B) ​the percentage of variance explained (r²) is large
C) ​both Cohen's d and r² are large
D) ​a significant effect does not necessarily mean that the effect size will be large