9. We first (meet) ________ in 2001. So we (know) ________ each other for 8 years.

The first blank needs the past simple of 'meet' because we have a specific time which is 'in 2001', so the past tense of 'meet' is 'met'. The second blank needs the present perfect because of the phrase 'for 8 years' which indicates how long this has been going for. So the present perfect tense of 'know' is 'have known'. Therefore, the answer is: 9. We first met in 2001. So we have known each other for 8 years.