Final answer:
An intellectual disability found in siblings, from lower socio-economic levels, and normal physical appearance is most likely genetic in nature.
Step-by-step explanation:
An intellectual disability found in siblings, from lower socio-economic levels, and normal physical appearance is most likely genetic in nature. Genetic intellectual disabilities are usually caused by abnormalities in the person's genes or chromosomes. These disabilities can run in families and are often present from birth or early childhood.