a. Prima propozitie este in Present Perfect, dar a doilea este in Past Simple.
b. already (Present Perfect), ago (Past Simple), last year (Past Simple), for months (Present Perfect), for ages (Present Perfect), during last summer's holidays (Past Simple), yet (Present Perfect), since 1996 (Present Perfect), several times (Past Simple), over the past few weeks (Past Simple), lately (Present Perfect), before (Present Perfect), recently (Present Perfect).