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04/05/2010 7:12 PM AEST | Updated 26/05/2011 5:45 AM AEST

The WORST Grammar Mistakes Ever (PHOTOS)

National Grammar Day was celebrated yesterday, March 4, 2010.

It was a great day to review the subject of grammar, whether you loved or hated it in school.

On National Grammar Day, it's worth watching a rendition of Conjunction Junction. You might stop by the New York Times' grammar tips for today. And teachers might want to visit Grammar Bytes for related exercises, handouts, and presentations.

In honor of the occasion, HuffPost Books has compiled some of the most common grammar mistakes in the English language.

Which of these bother you to no end and which aren't a big deal? Let us know by ranking these frequent grammar errors below.

Worst Grammar Mistakes Ever