"They can't paint."
Translation:Ők nem tudnak festeni.
Is it wrong to simply say "Nem tudnak festeni" ? In general is it okay to start sentences with "nem"? I felt like I saw people start sentences with "nem" in my previous Hungarian studies, but Duolingo does not seem to accept anything that starts with "nem" and I'm wondering if it is because it is not considered correct, or if it is simply because it needs to be added.
"Nem tudnak festeni." is correct. "Ők" is optional and it's not a problem to start a sentence with "nem".