——Bill has a lot of teaching experience, hasn't he?——Yes, indeed he has taught since 1950.或者He has been a teacher since 1950/ He has been in school sine 1950.时态为现在，Bill has a lot of ..... 指的是现在，所以回的也是现在，对现在造成影响了，以since 引导的时间状语从句，主句为完成时，又因为是现在的，所以用现在完成时。...
