"I would never forget that."
Translation:Das würde ich nie vergessen.
That's fine. The example given is one of those context-sensitive wordings. :)
Beginning with "Das" puts the emphasis on the unforgettable event or thing?
Yes and the wording is most commenly used when refering to a former sentence. "Hey, do you remember how you got stuck in that hollow tree?" – "Das würde ich nie vergessen. It was horrific."
Thanks. Duolingo has been using that structure a lot, it seems, and I wondered whether it was a matter of emphasis--as it would be in English--or whether something else was going on.