What gets me as a non-native speaker far more than "a vs an" is the "a vs the" conundrum. I still don't quite get when something needs to be "indefinite" and I've been speaking English for close to forty years. My native tongue lacks articles altogether and it's soo bloody hard I feel hopeless I'll ever master them fully.
But... "So do you want _a_ specific thing, or will any thing work?" sounds kind of correct as well to me. (Disclaimer: I am not native speaker, grain of salt and all.)
abraxas · · focus · HN ↗
arcbyte · · focus · HN ↗
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rawling · · focus · HN ↗
GP's should be used when offering a specific one, like "the red one".