Sure! Here are the corrections for each sentence with the mistakes underlined and corrected.

**9. I bought a cat in the market yesterday**
**Mistake:** "in the market"
**Correction:** "at the market"
**Corrected sentence:** I bought a cat **at the market** yesterday.

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**10. I have the cat. The cat is very nice**
**Mistake:** The sentence is grammatically correct, but it could use more variety or connection. If you want to keep the structure:
**Correction:** "I have a cat. It is very nice." (If it's meant to refer to the same cat, you can keep it, otherwise a more general statement works).
**Corrected sentence:** I have **a** cat. **It** is very nice.

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**4. Oanh had a hour to do her homework yesterday**
**Mistake:** "a hour"
**Correction:** "an hour"
**Corrected sentence:** Oanh had **an** hour to do her homework yesterday.