The fact that trisomies of only chromosome 21 and the sex chromosomes are ... ...

The fact that trisomies of only chromosome 21 and the sex chromosomes are observed in adults implies that:
(A) Chromosome 21 and the sex chromosomes are more prone to nondisjunction.
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in 18. Reproductive Systems, Gametogenesis, and Early Development