since-1,4,6,7,9,12,13,14
for-2,3,5,8,10,11,15
I have known Ben since my childhood
When have you started to work?
-------- since he entered the
------- have changed a lot since the last time
------- hasn"t been at work for week
+
How long have you owned this flat
I have taken part -------
-----------our secretary for several years
+