Read the sentences. Which phrases can we use to express gratitude in a semi-formal letter?

Phrases for expressing gratitude in a semi-formal letter:

1. I am very grateful for ...
2. I can't thank you enough ...
3. It gave me great pleasure ...
4. It was very nice of you to ...
5. Thanks a lot!/Many thanks!
6. I really enjoyed the ...
7. That's so nice of you!