**Core Concept**
The question is testing the diagnostic criteria for Major Depressive Disorder (MDD), a psychiatric condition characterized by persistent and intense feelings of sadness and loss of interest in daily activities. According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), MDD is diagnosed based on specific symptomatology and duration.

**Why the Correct Answer is Right**
To diagnose MDD, the DSM-5 requires a minimum duration of symptoms, which is essential for distinguishing MDD from normal grief or other conditions. The symptoms must be present for at least 2 weeks, with a minimum of 5 of the 9 characteristic symptoms being present, including depressed mood most of the day, diminished interest in activities, significant weight loss or gain, insomnia or hypersomnia, psychomotor agitation or retardation, fatigue or loss of energy, feelings of worthlessness or guilt, diminished ability to think or concentrate, and recurrent thoughts of death.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the DSM-5 does not specify a minimum duration of symptoms for MDD as 1 week. A duration of 1 week may not capture the full spectrum of symptoms and would not be sufficient for diagnosis.
**Option B:** This option is incorrect because the DSM-5 requires a minimum of 5 symptoms, including depressed mood, to be present for at least 2 weeks, not just 1 symptom.
**Option C:** This option is incorrect because the DSM-5 does not specify a minimum duration of symptoms for MDD as 3 weeks.

**Clinical Pearl / High-Yield Fact**
To remember the diagnostic criteria for MDD, the acronym "DEPRESION" can be used, where each letter stands for a characteristic symptom: D - Depressed mood, E - Energy loss, P - Psychomotor changes, R - Recurring thoughts of death, E - Feelings of worthlessness, S - Sleep disturbances, I - Interest loss, O - Others (diminished ability to think or concentrate), N - Nutritional changes.

**Correct Answer: B.**