"The apple is old and the peach is new."
Translation:התפוח ישן והאפרסק חדש.
So my answer -התפוח הוא ישן והאפרסק הוא חדש - was marked as incorrect. Was this because I was trying to use the copula? Was it wrong to use the pronoun (or did I make some other error)? Oy - I would really love to nail down this copula idea! :) Thanks for your help!
I've also tried to use copula. It seems this section has no examples using copula.
I put this question to the Duolingo Hebrew Facebook community, and some native speakers very kindly answered that it's not exactly wrong to use the copula in this case, but it's unnecessary (and unnatural?) since the subject is followed by an adjective. They gave a helpful rule to follow: if the subject is followed by another noun (as in, "the peach is a fruit"), then this (pronoun) copula would be needed.