MSFinals-5398

A 28-year-old man presents to his primary care physician with concerns about recurring thoughts. He has been experiencing thoughts of needing to repeatedly check that his car is locked when leaving it, even though he knows he locked it. Sometimes he feels the need to physically check the car, but other times it is just thoughts. He denies any symptoms of depression or psychosis and has no significant medical or family history. He is not taking any medications. What is the recommended first-line treatment for his likely diagnosis?