An intellectual disability in which no evidence of brain damage or genetic disorder can be found is called intellectual disability.

An organic mental disorder or disability sometimes called OMD, has various names as organic brain syndrome or chronic organic brain syndrome, this is a type of reduced mental capabilities which are a result of a medical or physical problem instead of psychiatric issues.

d. i assume the underlined word is "role." reformat if it isn't.

explanation:

role is closest to part because when replacing words, "playing a vital decision," "playing a vital activity," and "playing a vital dollar" don't make logical sense. the only meaningful choice is "playing a vital part."

this fits one of merriam-webster's definitions of role: "a function or part performed especially in a particular operation or process."

you answered your own : -/