Here are the corrections for each sentence:

1. **My cousin is the same age of me.**
- Correction: C (should be "as me" or "as I am").

2. **Would you like any eel soup for lunch?**
- Correction: B (should be "some" instead of "any" for affirmative questions).

3. **They built the Sydney Opera House for 1973.**
- Correction: D (should be "in" instead of "for").

So the letters to circle are: C, B, D.