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Which is the correct way :

"The present invention provides a method and AN apparatus for.."

or

"The present invention provides a method and apparatus for.."
?

Thank you
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'Apparatus' is singular and plural, and has the alternate plural 'apparatuses'. If there is more than one piece of equipment, leave the article out or, better, change to the '-es' plural; if there is only a single piece, add the article for clarity.