I think duo needs to make a decision on what to call the second meal of the day and leave it at that.
I feel it really tries to make a point that those things are complicated :). But it should accept all correct answers. And second meal is II śniadanie :)
If Im correct obiad is not a dinner? Or am I wrong, cause it did not let me pass cause I did not choose both kolacja and obiad.
This is complicated. I guess for you dinner is evening meal, which means only kolacja is right word for it. but duolingo sees it different. https://www.duolingo.com/skill/pl/Food-1