"Bisher fällt uns jedoch kein wirklicher Kracher ein."
In one of the real-world translations, the best translation for the sentence above is: "So far, however, it does not strike us as a real firecracker." This "best" translation is incorrect, but entering a correct translation, such as "So far, however, we couldn't think of a really good idea", is said by Duolingo to be wrong. How does Duolingo decide whether a translation is right or wrong? Is it by comparison with the "best" translation?