Option B 'met' is correct. The phrase 'last week' indicates a specific, completed past time, requiring the past simple tense. 'Met' is the past simple form of 'meet'. Option A 'have met' (present perfect) connects past to present, which doesn't fit because speaker says 'not so sure'. Option C 'was meeting' suggests an ongoing action, not a single encounter. Option D 'had met' (past perfect) requires a previous past time reference.