In English you talk about "preparing" without any object, but not in Spanish. So if you aren't preparing something in particular, you have to use the reflexive.
Also you could translate this as 'They have been prepared there," which is accurate and Duolingo accepts. It's the passive use of the reflexive.
My "they have been prepared there" was not accepted" . Should I have added the fullstop??
Do all Spanish verbs work this way? If there isn't a verb specified, then it is reflexive?
Hola Amigo duolearner12345: A reflexive verb is one in which the action reflects back upon the subject. Some verbs are always reflexive and will be shown that way in a dictionary: bañarse, for example, and will marked by the "se" on the end of the verb. Others are not always reflexive, but can be made reflexive by adding the "se" (like in the sentence we are talking about on this page). There are other uses of the "se" like making the verb passive instead of active, but that is another semester. So, in this sentence, look for the "se". When the verb is conjugated the "se" is removed from the infinitive and placed in front of the verb. You can think of the "se" as "themselves" although you do not have to translate the actual word. In other sentences, the "se" could also mean "himself", "herself" or "yourself" or "yourselves" depending on context. So, literally this sentence could be translated: "There, themselves they have prepared." but that doesn't sound right in English, so we just change the word order a bit and get: "There they have prepared (themselves)"
Is this the general case for Spanish reflexive verbs? That (assuming there aren't other markers in the sentence to clarify the distinction) there is ambiguity in the meaning of sentences with reflexive verbs: it could be that the object of the verb is the speaker, or it could be that the sentence is in passive voice?