"We roast some sweet potatoes."
Translation:Arrostiamo qualche patata dolce.
Did you include the adjective "dolci?" When discussing these lessons, it is important to include an exact copy of one's answer so that everyone can evaluate the entire situation. Then, everyone will be able to fully understand the situation and learn from it and perhaps help. Without knowing what you and others entered, we do not know where the problem exists -- yours or Duolingo's.
Here is the conjugation of "arrostire:" I roast = arrostico; you (singular) roast = arrostici; he/she/it roasts = arrostice; we roast = arrostiamo; you (plural) roast = arrostiti; they roast = arrostiscono.
Here is a link to a site that will conjugate Italian verbs: https://conjugator.reverso.net/conjugation-italian.html
Edit: "Arrosto" is an adjective or a noun meaning "roast." Here are examples: "I eat the roast lamb" translates as "mangio il agnello arrosto;" "I put the roast in the oven" translates as "metto l'arrosto nel forno."
This is exactly what I wrote above, and the other comment too for arrosto. It would be great if people could read everything before commenting, to avoid duplication. FWIW my comment was answered, and although it's not completely obvious when this will apply, it is consistent. We learned Costruire, which also has "io costruisco" and then "noi costruiamo".
Although Duolingo does provide a little guidance in the early lessons of some topics, it does not explain many things. That is the way this style of learning works. If Duolingo did explain everything, it would have to provide a textbook. Fortunately, there are forums like this one where students can help each other. Although I have several textbooks and refer to them occasionally, I usually find the forums more convenient. Furthermore, some forums cover things that aren't in the textbooks that I own.
By the way, in Italian, the word for potato (patata) is a regular feminine noun. The plural of "patata" is "patate."
When one uses "qualche" the following noun and any adjective must be singular even though the meaning is plural. However, if one uses "alcune," not "qualche", the following noun and adjective must be plural because the English sentence uses the plural "potatoes." So you should have written "alcune patate dolci.
You used singular words. See thesoph33's comment at the beginning of this forum. He said "I wrote this and it was accepted - arrostiamo delle patate dolci." Notice that he used plural words: delle, patate, and dolci. If one uses the word "qualche" as the word for "some", one must use singular words to which the word "qualche" refers. Otherwise, one must use plural words.
Nicola, these forums definitely help one learn a new language. Sometimes they become very large and, as a result, it can be difficult to find an answer to one's question. When people ask questions that have already been answered, they add to the bulk of the forum and make it difficult for others.
Your question has been answered in several ways. Please take the time to look through the forum. Thank you.
Close, but not quite. "Patate" is plural as is "delle." However, the adjective "dolce" (sweet) has only two forms: "dolce" (singular) and "dolci" (plural). Since "delle patate" is plural, the plural form of "sweet" (dolci) must be used. Thus, the correct phrase is "delle patate dolci."