A 2.6.9-ac1 kernel would be

A 2.6.9-ac1 kernel would be

A.
an unstable kernel.

B.
an alpha kernel.

C.
a stable kernel.

D.
someone’s patch to an unstable kernel.

E.
someone’s patch to a stable kernel.

Explanation:
This file is the patch file for security bugs of 2.6.9 version kernel.