Here’s how the phrases can be matched with suitable purposes of communication:

1. **Write an email to:**
- **1 - reply to your friend’s email**: **D - I’m happy to hear from you.**
- **2 - invite your friend to a party**: **C - Would you like to …?**
- **3 - suggest your friend to do something**: **B - Why don’t we …?**
- **4 - ask your friend about something**: **A - Do you know if …?**

Feel free to ask if you need further assistance!