I said I would be her exclusive driver, and the girl replied, really? What should I say?

If he asks this question, he may be too surprised, or too surprised to believe, and then ask, really? I want to make sure.

At this time, you can say, of course it's true, how could I lie to you?

Then the girls will be very happy to hear it, hmm.

You can also say.

I am very sad to ask, don't you believe me?

Of course what I told you is true. This is the way to prove that what you said is true.