A 50-year-old man with recurrent major depressive disorder has been taking sertraline at an adequate dose for 8 weeks with partial but insufficient response (about 30% symptom reduction). According to CANMAT, which is the best next step?ADeclare treatment-resistant depression and stop all medicationsBImmediately switch to electroconvulsive therapy without further trialsCOptimise antidepressant therapy by dose adjustment or switching/augmenting, using a systematic, measurement-based approachDContinue the same dose indefinitely despite partial responseEAdd a benzodiazepine onlyCheck my answer