Why Can't Heritability Estimates Be Used to Explain Group Differences

Why can't heritability estimates be used to explain group differences in intelligence?

A) Heritability estimates can only be used to predict individual variation from standardized test scores, and do not apply to group differences.
B) Heritability estimates apply only to characteristics that are determined by a single gene or gene pair.
C) Heritability estimates can only be applied to differences within a particular group, because environmental conditions vary for different groups.
D) Heritability estimates only apply to intelligence scores that are averaged over a period of at least 20 years, and group data does not exist for that period.