thanks for answering my question...do u know a website i could go to to learn about the different variations?

5...Nxe4 is a viable option to which White normally replies 6.d4.

Keres played 5...d6 more often, but played both. He had better results with 5...d6: eight wines, five losses, four draws.

I've found six games in which Paul Keres played 5...Nxe4. He had an even score with that variation: one win, one loss, four draws.

Here's the win:

why didnt black play 5. Nxe4...