In order for a human female to express a recessive sex-linked trait, she must
a) two recessive alleles
b) an inactive allele
c) a recessive allele on a y chromosome
d) two recessive autosomal alleles

In order for a human female to express the recessive sex linked trait, she must have A. 2 recessive alleles each on her X chromosomes. Assuming complete dominance of alleles on sex chromosomes is followed, and observed, this is tue only particular way that females can phenotypically showcase the trait, as a presence of a dominant allele on any one of her X chromosomes would mask the gene product produced based on the recessive allele, and thus can't be observed phenotypically.

The solution is A.