The attached earlobes are a recessive phenotype, which indicates that only someone that has two recessive alleles for the trait will show the phenotype.
If "R" is the dominant allele and "r" the recessive allele, the genotype of the female that expressed the recessive phenotype will be "rr"
For the child to have the recessive genotype, it must have inherited one recessive allele from each parent. This means that both parents must have at least one recessive allele "r"
Out of the four options, the only one where the genotypes have at least one recessive allele is option b.