5) C

Let the dominant allele be (T )and the recessive allele be (t)

T                                  t

T                      TT (33%)                   Tt (66%)

t                       Tt (66%)                    tt (dead)

There can only be two genotypes present in live offspring. The fetus with genotype (tt) will die.
Possibility of homozygous dominant (i.e. TT) = 1/3 = 33%