Given that the meaning of the Spanish phrase is clear, a point of English grammar: A single "it's/It is" cannot reference both an adjective and a verb form, e.g. "dark and raining". It could be "It's dark and rainy" or "It's dark and it's raining" or some variaton of the latter. Reported.
"Está oscuro y lluvioso." = "It is dark and rainy." (adj + adj) The adjective + adjective form would be English. Does it work in Spanish? I think I have learned that in Spanish the "está" is only connected to the "oscuro" and the "llueve" is an independent subject and predicate in that special Spanish way of dropping off the subject pronoun.
Duo does use hace at times: hace calor/frio/sol I have seen for example. But here there are no nouns- oscuro/dark is an adjective hence está (I assume because "it" will not always be dark) and llueve is a verb - it rains so hace woyld be meanungless either part. I tbought your English translation was the correct one tbough. See comment below also.
"It's dark and rainy" sounds better because it is a more parallel expression in English. (An adjective phrase "It's dark" and a verb phrase "It's raining" are not parallel constructions. ) Duo's suggested translation of "It's dark and raining" sounds to my ear more like someone saying, "It's blue and falling."
RyagonIV, both English sentences are appropriate translations from that sentence in Spanish.
Further, looking at translating similar sentences from Spanish to English (from Google Translate, Span(i)shD!ct, etc:
It is dark and raining. - - Esta oscuro y lloviendo;
It is dark and rainy - - Esta oscuro y lluvioso;
It is dark and stormy - - Es oscuro y tormentoso. (I'm not quite sure why the verb changes)
Está oscuro y llueve - - It's dark and it's raining;
Está oscuro y llueve. - - It is dark and it rains. (Apparently, ending the sentence with a period changes the recommended word in English).
Está - to be;
oscuro - dark;
y - and;
llueve - to rain
At times we are marked wrong for choosing formal language responses and other times, for choosing natural language or idiomatic responses. Is there some way you could help us in trying to guess what you and the others intend with a response (formal, informal, natural, idiomatic, or slang)?
The sentence "It is dark and rainy" is an appropriate translation of "Está oscuro y llueve", but within some boundaries. These two sentences are likely the most natural ones in their respective translations. However, Duo wants to (or at least needs to) be more precise when it comes to translating, and since llueve is a verb, it should be translated as such in English, too.
That putting a period on the end of a sentence changes the translation should tip you off that automatic translators are not very reliable when it comes to grammatical detail. :)
"Está oscuro y lloviendo" sounds a little strange, just like "It is dark and raining", since you're mixing an adjective with a participle here as well.
The verb change in "Es oscuro y tormentoso" implies that it's describing a specific object. It's hard to imagine a concrete object being "stormy", but tormentoso can also mean "full of tension and conflict", so this sentence could refer to a dark and troublesome time.
Llueve is a conjugated form, by the way. It means "it rains" or "it is raining". The infinitive "to rain" would be llover.
My recommendation for translations on Duolingo might be a bit paradoxical at times. Write what's natural in English but make sure it expresses the exact same as the Spanish sentence. So if you're tasked to translate "Leemos un periódico", you shouldn't say "We are reading the newspaper". Even though it's more natural, the Spanish sentence isn't talking about a specific newspaper. If you're translating "Nos gusta el tiempo", you shouldn't say "The weather pleases us", because it's not natural. Make sure to learn the common translations for words and phrases like gustar, encantar, "a veces", "hacer la compra", and so on.
The most common pronunciation for the 'll' digraph is similar to the English 'y' (IPA: [ʝ]), but it's by far not the only one. If you go south in South America, you can hear it being pronounced closer to an English 'j' [ʒ] or a 'sh' [ʃ] sound. And some places, which retained the original pronunciation of 'll', pronounce it as a palatalised 'l' [ʎ] (an 'l', but instead with your tongue tip against your teeth, the middle part is pressed against your hard palate).
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