Most commonly associated disorder with Down's syndrome among the following is: (A) Hirschsprung disease, (B) CML, (C) Late onset Alzheimer's disease, (D) Early onset Alzheimer's disease
Answer is D. Among the following options, Early onset Alzheimer's disease is most appropriate.

AML & ALL have equal incidence
Duodenal atresia is most Common GI disorder associated with Down's syndrome.
Early onset Alzheimer's disease (Pre-senile Alzheimer's in associated with Down's syndrome.