"The beds are not in the market."
Translation:Lecti non sunt in foro.
The negative particle, normally, is used right before the word it negates (some exceptions do exist, but it's good practice to follow this rule, as it allows us to understand what is negated - usually it's the verb)
Lecti - non in foro sunt. Maybe it could work to put the emphasize on "in foro" as the place they are certainly not?
I just confirmed that Lecti non in foro sunt is in the answer database, which means you had an error somewhere. From now on, please either copy and paste or take a screenshot of your full, exact answer so we can help you see the real reason why it marked you wrong.
For the record, the following are all accepted:
- Non sunt lecti in foro.
- Non sunt in foro lecti.
- Lecti non sunt in foro.
- Lecti non in foro sunt.
- Lecti in foro non sunt.
- In foro non sunt lecti.
- In foro lecti non sunt.
Nominative vs accusative (subject vs direct object).
Here is a plain-English overview of what the cases are and how they work:
Latin cases, in English
Adjectives must agree in gender, number, and case with the nouns they modify, but they have their own declensions. Sometimes you get lucky and the adjective just happens to follow the same declension as the noun, but that is not a guarantee.
"Forum" is 2nd declension neuter. The form "forum" is the nominative, accusative, and vocative. The form "foro" is dative and ablative, and in this case (no pun intended) it's the ablative because it's the object of the preposition "in".
We're not equating "beds" to "in the forum". Saying X=Y would be when you use the predicate nominative. We're saying where they are located. And being the object of the preposition "in" requires the ablative here.
Please see my other comment for links and explanations.