Answer:
A. Individual #8 must be heterozygous for the trait.
Explanation:
Since the given trait is autosomal recessive, two normal but carrier (heterozygous dominant) parents can have the affected progeny. Individual 8 and individual 9 have affected son and daughter. Hence, both of them should be heterozygous dominant and carry one recessive allele to transmit to the affected progeny.
Individual 10 is affected with autosomal recessive trait and hence is homozygous recessive. Since individual 13 has two heterozygous recessive parents, it may or may not be homozygous for the dominant trait. Individual 3 have affected progeny and hence should be heterozygous dominant for the trait.
