urrgghh why is duolingo so keen on promoting america :(
the dictionary hints list "bora" as either best or better but marks the sentence wrong it we use best.
I see "American technology is the best" as the given answer above, so I'm not sure what happened on your end.
"American technology is best" is marked a wrong: "the best" is accepted.
bora can mean better, best, excellent, brilliant, etc. So they should all be accepted
Duo has clearly never been to Japan.