A 45-year-old man with depression treated with sertraline for 6 weeks shows partial response but remains significantly symptomatic. He has tolerated treatment well. According to CANMAT guidance, what is the most appropriate next step?AStop sertraline and start another SSRI at low doseBIncrease sertraline dose if not yet at maximum toleratedCAdd a second antidepressant immediatelyDStop medication and switch to psychotherapy aloneEDeclare treatment failure and refer for ECTCheck my answer