if one alien ask me where u from? what to say?

None of these options are accurate. Let's look at them individually:

'1. i can say humans are in earth some billions years ago'

All life formed from non-living materials billions of years ago in a process known as abiogenesis [1], but we humans only evolved within the last few hundred thousand years.

'2. we humans from monkey'

We do not come from monkeys, although we are very closely related to them.

'3. we humans from god(Adam and Eva)'

There is no evidence for Adam and Eve and all evidence points against it.

'4. we from asteroids to earth'

Panspermia? [2] Very unlikely. Any living or dormant life would have been burnt upon entering the Earth's atmosphere. Some amino acids may have come from this source, but they are also common on Earth.

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Instead, I would say to the alien that we originated as unicellular life by a complex process known as abiogeneis (not fully understood), 3.5 billion years ago. Incredibly, we have evolved to sentient life incrementally over the course of this time, and this is how I communicate to you today.

Obviously there is much more to say, but the above would serve as an introduction.

Presumably an extra-terrestrial species that has mastered space travel will be advanced enough to have figured out that life evolves. Furthermore it is possible that they have observed us since the beginning and know our origins with even more certainty that we do.

If, however, an alien really did ask me that question I would tell him that we evolved from apes, not monkeys.

Wow, erm, I'd avoid opening your mouth to talk to the alien..and most certainly not try to talk with it over chat. It might get the wrong impression about the human race (although, I've lost faith in it myself).

I'd say "I'm from Arizona. Let me see your proof of citizenship!"

berwyn.