Is there a general rule of thumb for the use of "While" at the beginning of a sentence? For example:
"While Justin likes to pay for food with cash, Mark likes to pay for food by VISA." What is wrong with this sentence that marks would be deducted? I was told to change the word "while" to "although" to make the sentence correct. Comments? (note: this sentence was changed from a technical report to the above in order to make it simpler to understand)

nit-pickers (eggs of lice)

knit-pickers (sounds like they fiddle with their sweatersEmotion: stick out tongue)

This is a case where "while" means "whereas". It's a normal use of "while". I don't know why it was considered incorrect.

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Your sentence seems correct to me. (Note that this use of "while" is rather formal and literary, and may seem out of place in everyday conversation.)

I think it would be safer to quote the exact words of your original sentence.
Thanks for your help. Professors can be such knit-pickers at times looking for anything to deduct marks with!!!
 Clive's reply was promoted to an answer.
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 CalifJim's reply was promoted to an answer.