I'm not sure, but I think... 我不能确定，但我觉得……
1. I'm not sure, but I think we should have more discussion on this.
2. I'm not sure, but I think the final exam is on the morning of next Monday.
3. I'm not sure, but I think we can have a bargain with the owner.
A: Wow! That's a fantastic movie!
B: Yes. I love it, too.
A: Who was the director?
B: I'm not sure, but I think it must be directed by Zhang Yimou. That's typical of him.