In a family, the third child showed Down's syndrome but neither of the parents nor siblings of the affected child manifested symptoms of the syndrome. The possible reason for the Down's syndrome only in the affected child is:

Options

1. Aspontaneous mutations in the DNA of the child due to environmental factors.
2. Bchromosomal segregation defect during ovum development in the mother.
3. Cchromosomal segregation defects in the cells of the uterine wall of the mother during foetus development.
4. DDNA replication defects in the child resulting in translocation of chromosomal arms.