I'm sure that they must have visited the place before帮忙翻译下.

I'm sure that they must have visited the place before帮忙翻译下.
I'm sure that they must have visited the place before帮忙翻译下.

I'm sure that they must have visited the place before帮忙翻译下.
我能确信,他们以前一定来过这个地方.

我确定他们以前肯定来过这个地方

我确定他们以前就曾经来着旅游过/拜访过。

我确定他们以前一定来参观过这里。

我肯定他们以前绝对去过那个地方。