When there are no known genetic or organic influences, the causes of intellectual disability are generally considered to be

I believe the answer is: cultural-familial

cultural-familial refers to the mental deficiency that is caused by the culture where the person grow up rather than genetics.
Examples of cultural-familial factors are: mental deficiency because wrong way of parenting, mental deficiency because of poor socialization, etc.

Ibelieve your answer would be answer choice a