What Is the Underlying Assumption of the "Structure" Method for Analyzing

What is the underlying assumption of the "structure" method for analyzing multiple loci at the same time?

A) It assumes that the number of genotypes under consideration comes from an unspecified number of distinct groups, each with its own characteristic allele frequencies.
B) It assumes that an undetermined number of genotypes come from a specified number of distinct groups, each with different allele frequencies.
C) It assumes that the set number of genotypes under consideration comes from a specified number of distinct groups, each with its own characteristic allele frequencies.
D) It assumes that the set number of genotypes under consideration comes from a specified number of distinct groups, each with different characteristic allele frequencies.