Based on this information, what is Ace's phenotype for the horns trait?

 - not having horns
 - having horns
Ace's genotype for the horns gene is hh. Ace's genotype of hh has only h alleles. The h allele is for having horns. So, Ace's phenotype for the horns trait must be having horns.
To check this answer, consider whether Ace's alleles are dominant or recessive. The allele for not having horns (H) is dominant over the allele for having horns (h). This means H is a dominant allele, and h is a recessive allele.
Ace's genotype of hh has only recessive alleles. An organism with only recessive alleles for a gene will have the recessive allele's version of the trait. So, Ace's phenotype for the horns trait must be having horns.