What's the difference?

[Brightsun]

What is the difference between 1 and 2?
1. I haven't visited America before.
2. I didn't visit America before.
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1. I have once eaten this food.
2. I ate this food once .

Thank you so much!

[Teia]

What is the difference between 1 and 2?
1. I haven't visited America before. - the speaker might go to America sometime.
2. I didn't visit America before.- the speaker does not state his wish to go to America sometime.-he simply makes a statement.

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1. I have once eaten this food.
2. I ate this food once .

Thank you so much!

1. present perfect simple - unspecified time of action
2. past tense simple - finished action