Mark which of the following are opening remarks (O), and which are closing remarks (C)

1. Thank you in advance for your help.
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2. Please write back soon with the information.
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3. I am writing to ask for some information about the karate lessons which I saw advertised in this week's Black Belt magazine.
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4. I saw your advert in Sports Illustrated and I would like to know more.
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5. I look forward to hearing from you soon.
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