Here are the completed expressions based on the dialogue:
1. Giving your opinion
* a. In my opinion, I think we should have...
* b. The way I see it...
* c. Personally, I prefer vegetarian burgers.
2. Responding to other people's opinions
* a. Maybe you're right.
* b. That's a good idea.
* c. Yes, I agree.
3. Asking other people's opinions
* a. Why don't we go to the new fast food place?
* b. What about the seafood restaurant?
* c. What do you think about going for pizza?