Translation:Smart people cross at the crosswalk.
Yes, I agree with the comment below. This is a Duolingo disaster. We never say crosswalk. I see that some Americans claim that they do but no-one would use this expression in the UK. If it's acceptable, I would strongly argue that the word "crossing" is equally so but it wasn't accepted.
I can't resist this and I'm guessing vvsey will know what's coming. In this instance, smart or clever is the characteristic much like intelligence. But what do we have here? "Az okos emberek etc..." In the example we had of intelligent people not jumping out of windows, there was no "Az" at the beginning. The distinction was between a quality possessed (i.e a characteristic) and the person or creature depicted (e.g a lion or a Hungarian politician) where "A" or "Az" would be essential. In view of the contrast between "Intelligens emberek etc...." and "Az okos emberek etc....." I'm left with the impression that the use of "A" or "Az" at the beginning in these instances is largely optional. If that's correct, I understand because many speech patterns are.