First of all, you are incorrect because OA is not D
Secondly, if IN YOUR OPINION it is D, we would like to hear how you come up with that. Do not waste people time in Math discussion with IMOs.
Trust me being polite/courteous towards others will not hurt u. Think about it for sometime and get back.....
Seriously, could u not have just said
Jack,
The OA is
A. If you could help me understand your thought process on D we could discuss further.
Please dont make things more complicated than what it really is in terms of communicatiing!!!
Thanks! Have a great day!!!

Extra smiley just for u buddy!