1. I have lost my keys. I can’t find them anywhere.

Explanation: We use Present Perfect because the result is important now (the keys are still missing). There is no finished time mentioned.

2. We visited the museum last weekend.

Explanation: Past Simple is used because last weekend is a finished time in the past.

3. She has lived in three different countries.

Explanation: Present Perfect is used for life experience. The time is not finished and is not mentioned.

4. I have never visited Japan before.

Explanation: We use the Present Perfect to talk about a life experience that has not happened at any time up to now. The exact time is not important, only the experience.

5. They finished the project yesterday.

Explanation: Past Simple is used because yesterday is a finished time.

6. He has already seen that movie.

Explanation: Present Perfect is used with already to show something happened before now, with no specific time.

7. We met our English teacher last year.

Explanation: Past Simple is used because last year is a finished time in the past.

8. She has written five emails so far today.

Explanation: Present Perfect is used because so far today means the time period is not finished.

9. I didn’t understand the lesson last Monday.

Explanation: Past Simple is used because last Monday is a specific, finished time.

10. They have been to France twice.

Explanation: Present Perfect is used to talk about life experience without saying when it happened.

11. He bought a new phone two days ago.

Explanation: Past Simple is used because two days ago is a finished time.

12. We haven’t decided yet.

Explanation: Present Perfect is used with yet to talk about something that has not happened up to now.