past simple vs. present perfect

[MiaL]

Hi,
I would like to know how to use the above mentioned tenses corectly in the following situations:

- Two people are talking to each other. One says something, but the other doesn't understand him. Does he ask. "What did you say?" or "What have you said?" What is the difference between the two uses?

- One of the above mentioned sees / hears a car and asks the other one: "Have you seen / heard ...? or "Did you see / hear ...?" Again, what is the difference?

Thank you very much for your answer,
Mia

[Hayseed]

Hi MiaL,
"What did you say" is best in that situation.
"What have you said" works as a question. You`re asking someone "What have you said about..." See the difference? Hope so!

"Have you seen the car?" You`d be asking someone if they had seen the car at some point in the past.

"Did you see the car?" The car just drove by, and right now you are asking someone if they saw it. Make sense?