Wow, that is indeed a tall order with a 500 GMAT. But, never say never!
What you write completely depends on YOU... Unfortunately, without really knowing you, we can't provide concrete feedback on what question you should choose or how to start you essay. If you're really stuck, try asking yourself those three questions, and see which ones leads to an answer that easily flows out of your mouth. (Literally ask yourself out loud, and answer using your own words.) That's a good place to start.
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