A team of scientists is studying the inheritance of eyelash length in humans. Eyelash length is either long or short, and is controlled by a single autosomal gene. The eyelash lengths of the members of one family are shown in the pedigree below. The pedigree labels the generations I, II, and III. The male and female in Generation I are the parents of the three males shown in Generation II, and the grandparents of the three females shown in Generation III. Which of the family members MUST be heterozygous for the trait of eyelash length, meaning their genotypes include one allele for long eyelashes and one allele for short eyelashes?