Children diagnosed with severe intellectual disability (e.g., IQ = 50), tend to have siblings who have IQ scores around 100, whereas children who are diagnosed with moderate intellectual disability tend to have siblings who have IQ scores around 80. We can conclude that:
A) Severe intellectual disability runs in families, but moderate intellectual disability does not
B) Moderate intellectual disability runs in families, but severe intellectual disability does not
C) Intellectual disability is completely dependent on the environment
D) Intellectual disability is highly heritable