One disease-causing agent that has been associated with various forms of mental illness, including schizophrenia, obsessive-compulsive disorder (OCD), and generalized anxiety disorder:

	a.	is genetic and could be inherited from both parents if the disorder is heritable.
	b.	is a parasite that lives in the intestines of about 40% of household cats.
	c.	is a certain type of vaccine that has also been linked to autism.
	d.	can be the type of therapy received to treat the psychological disorder.