I am in the US - pants = trousers. I do know in the UK that pants are equivilant to underwear, but especially in a timed practice, my first thought is to put pants. Both should be accepted.
This is rather frustrating for us, we deleted this particular sentence because it didn't fit in with Duolingo's preferred style of starting each phrase and sentence with a capital letter. We replaced it with the phrase 'Trowsus newydd' which includes the option to answer 'New pants.
Now we find that Duolingo has continued to present the deleted sentence to people without the option to answer new pants.
So apologies for Duolingo creating frustration with this question.