Having strong nails is completely dominant to having brittle nails. However, the brittle nail genotype shows a 75% penetrance for the brittle nail phenotype. This definitively means that a man with strong nails:.

The given question is incomplete as the multiple choices were not given, however, the correct options for the question as follows:

You can answer more than one choices-

A. has a diploid genotype in which both alleles are for strong nails

B. has a heterozygous diploid genotype.

C. has a diploid genotype in which both alleles are for brittle nails

D. has a diploid genotype in which both alleles are unknown

The correct answer is - option A  has a diploid genotype in which both alleles are for strong nails and

option B. has a heterozygous diploid genotype.

Explanation:

Let assume S is dominant over ''s" allele. Dominant S allele represents strong nail phenotype.

It is given that strong nail trait is completely Dominant over brittle nail phenotype. But the penetrance for brittle tait phenotype is 75 percentage.

But diploid with SS or Ss ( heterozygous) have strong, type of nails phenotypically.

Thus, the correct answer is - option A  has a diploid genotype in which both alleles are for strong nails and

option B. has a heterozygous diploid genotype.