trading techs with AI Civ

[Nethog]

I am new to Civ 2 and have a question regarding trading techs with an AI Civ.

When the AI asks me to trade a specific one of their techs for one of mine why do I then get to pick from a window that lists several of the AI's techs (including the one they offered originally)? Why do I get to pick when I already agreed to take the one they offered? What happens if I pick a different one?

[Caesar the Great]

Nothing happens if you pick a different one, you simply get that technology. I'm not sure why they made it like that, but if you trade techs you can choose the tech.