All my teachers

Which would be correct if the person speaking is accepting a prize (eg. an Oscar) and he hasn't had a teacher for a very long time:

1) I would like to thank all my teachers.
2) I would like to thank all those who were at one point my teacher.
3) I would like to thank all those who were at one point my teachers.
4) I would like to thank all those who have been my teachers.

Do '2' and '3' imply that the people he is thanking were teaching him at the same time?

In that case, they won't work.

Gratefully,

Navi