Translation:Vegetables are different from animals.
Different to is, apparently, correct, but more common in British English than American. I've never heard it and had to look it up.
In American English I hear "different than" about as often as "different from". Duolingo accepted it in my translation of the above sentence. The American Heritage Dictionary, in a short article at the entry for "different", says that it is found in the writings of many reputable authors.
Vegetables are masculine: http://www.french-linguistics.co.uk/dictionary/legume.html
Why is there a "Les" instead of "Des" at the front of this sentence? It seems more likely that we're making a statement about vegetables and animals in general, than about a specific set of vegetables being different from animals. Using "Des" would still leave us with the required article at the front.
la/ le/ les has two meanings.
la/ le/ les ....specific, those ones right there
la/ le/ les...general, all examples of something
In this case it's all examples of vegetables are different from animals.
In English we don't have the use of the in a general sense because we simply drop the article when we want to indicate all examples of something. We just say vegetables not some sort of article in front of vegetables which indicates general.
English ....vegetables are good means all vegetables are good.
But French requires an article in front of the noun therefore the French have given the role of a general article to la/ le/ les as a second meaning.
That is why Duo sometimes drops the article from the English translation and other times steals a heart from you if you don't include it.
The only way to tell the intended use of la/ le/ les is by the context of the phrase.
This is most helpful, and I think clarifies several situations in which I've wondered why a seemingly non-specific le-form was used. So le refers not only to a specific (set of) things but also to all things of some form, whereas des refers to an unspecified (sub)set.
Given that all things meeting some criterion is also a specific set, just specific in some other way, the logician in me applauds this rare case of a language making more sense than I dared expect!
Years ago, Duo had a token system. Symbolic hearts were awarded but taken away for incorrect answers. Lose three hearts in a lesson and you had to repeat it. Thus you could get everything right in a lesson but lose three hearts for one tricky concept that wasn't well explained. Some students would have to repeat a lesson three of four times before finally finding a satisfactory explanation in the comments.
Sometimes the loss of a heart seemed inconsistent or the result of unfair expectations. Comments such as ...How could I know that?... as well as ....the same answer was accepted in another example?.....