1)How long have you known Mike? I've known him since we were six.
2) How long has your uncle been a doctor? He's been a doctor for many years.
3) How long has Clive had a pet dog? She's had her dog since last Christmas.
4) How long have they followed Manchester United? They've followed Manchester United since they saw them play live.
5) How long has he held the 100 metres record? He's hold the record since the OIympics.
6) How long have you played the piano? I've played the piano for five years.