Mistake in French
"The grapes are red." is corrected as a singular translation.
First, you should give us all details.
Second, you may think it is a mistake, but many words are singular in French and plural in English, and vice versa. Les poissons = the fish. Le raisin est rouge = the grapes are red.
Grape = grain de raisin.
The grapes are red = les grains de raisin sont rouges = le raisin est rouge.
'Les raisins sont rouges' is not a valid translation.
Thank you. I think I get it now. One more thing: do you ever say 'a grape' or does it have to be 'a grape grain'?
'Raisin' is the fruit in general. So, to talk of one grape, we say 'grain de raisin'. To talk of a bunch of grapes, we say 'grappe de raisin'. As you can see, it is the French word 'grappe' ('bunch') that eventually gave its name to the fruit in English, in the Middle Ages.
It's not so much that fish is only singular as it isn't inflected when plural, so it is plural, it just looks the same as the singular form. It is indeclinable.
I would note that fish probably isn't the best example, as fishes does exist. It was historically a plural form, and retains a moderate amount of currency, though now it is mostly reserved for biological contexts when referring to several species of fish. Many normally invariant nouns do decline in this context.
There seems to be a trend, particularly with animals, that the singular form replaces the marked plural form. This probably has a lot to do with how simplified modern English has become and that many animals of human importance were always invariant.
I know how complex it is. I only meant that the expected translation for 'les poissons (dans le bateau)' is 'the fish (in the boat)'.
I left a more detailed comment afterwards, but it is expected that you respond to 'The grapes are red' as'Le raisin est rouge.'Why not 'les'? I understand about a singular bunch of grapes, but clearly i'm still confused. Thank you.