Is saying "Do they eat bad fruits" wrong.... i guess my problem is in english rather than esperanto
This is an odd bit of English where singulars are used as mass nouns. There a similar distinction between fish/fishes. In the sense of the sentence, where you're not trying to distinguish between types of fruit, you'd use "fruit."
To match with "fruktojn." It's a plural accusative. [Bad fruit] is the recipient of action of the verb [eat], so it gets the accusative. Same as "he sees bad fruit," li vidas malbonajn fruktojn.
It is in the direct object. Rule 3 from La Fundamento says in part: Adjectives… The numbers and cases are the same as in substantives
Do they eat bad fruit habitually, or are they eating bad at the moment, or do they have the bad fruit almost in their mouth and you are deciding whether to to tell them or left them find out on their own?
Seems like there might be some chance the question would be "Are they eating bad fruit?".
"Do they eat bad fruit?" seems like a wording with a low probability of me ever hearing it said, compared to related questions "Did they eat bad fruit?",
It's an example, so not terribly real world. "Are they eating bad fruit?" is a perfectly good translation of the sentence, "Ĉu ili manĝas malbonajn fruktoj?" It could be offered as another alternative. This whole thread started on why it isn't "bad fruits."
You are right that "are they eating bad fruit?" is a more natural sentence. Something.
Unu: Ho, ili manĝas fruktojn! Du: Jes, kial? Unu: La fruktoj en la domo estas malbonaj! Du: Vere? Unu: Jes! Ĉu ili manĝas malbonajn fruktojn?
Because cxu marks it as a yes or no question. English doesn't just let you stick a question mark on the end and call it a day
right, but i can say, "They eat bad fruit?" in english and still get a yes or no answer
Okay, but Esperanto doesn't recognize the raised voice as a valid way to make a question.
Duo also does not take punctuation into account (so if you use the wrong punctuation but the correct words and spelling you don't get it wrong), so that's another reason why you can't leave it as "They eat bad fruit?"
As I noted above, "fruit" in this sense is a mass noun; a singular noun referring to multiple items. Since it's not referenced to a counted quantity, but instead the abstract idea of fruit, it's construed in the singular.
There are some cases in which both forms are grammatically correct, depending on meaning. >How much fruit did you buy? >I bought seven apples.
>How many fruits did they have? >Just three: apples, bananas, and strawberries.
What's the difference between "bone" and "bona"? I always get mixed up...