Possible reasons

Which are correct:
1) Here is a list of the reasons he might have quit his job.
2) Here is a list of the possible reasons he might have quit his job.
3) Here is a list of the possible reasons he quit his job.

I think '1' is ambiguous.
It could mean:
a) Here is a list of the reasons why I am saying he might have quit his job.
and it could also mean '3'.

To me, '2' seems to mean
c) Here is a list of the possible reasons why I say he might have quit his job.
but I guess it could also be used instead of '1'.

Gratefully,
Navi.