[AUCTeX] \includegraphics completions

[eN_Joy]

I am running Auctex 11.83 on Emacs 21.4, when I do:
C-c RET inc TAB
I only see "include" and "includeonly" as the candidate completions, why
is "includegraphics" not listed? Also if I manually type
includegraphics, I don't get a file name completion prompt in the
minibuffer, is this the way it supposed to be?

I have googled the problem and saw similar reports, but seems there's no
definite answers.

My .emacs has these lines:

;;; AucTex mode
(require 'tex-site)
(setq TeX-auto-save t)
(setq TeX-parse-self t)
(setq-default TeX-master nil)
(load "preview-latex.el" nil t t)
(add-hook 'LaTeX-mode-hook 'turn-on-reftex)
(setq reftex-plug-into-AUCTeX t)
(add-hook 'LaTeX-mode-hook (lambda ()
                                (TeX-fold-mode 1)))
                                (add-hook 'LaTeX-mode-hook
                                'LaTeX-math-mode)



Thanks,

Jindan