I don't know what difference between two highlighted sentences? I think both of them are similar to each other, they don't have any particular time, and I applied the present perfect to them. But the answer of the second is the simple past.

I really need someone explain for me. Thanks in advanced.
The first has no definite past time; it is about personal experience.

The second has a specific past time, mentioned in the previous sentence: 'six years ago'.
Your reply means that the second question of A refer to the tour B took? In others word, A only wants to know what countries B visited in that tour in the second question.
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That's right.