Translation:If there were no sun, life would not be possible.
The problem is that it is applied hapazardly in the Engligh translations in the Dutch unit. There are other conjectural or counterfactual clauses where Duo requires the English indicative translation. Granted, these are obscure and tortuous shades of meaning in both languages.
In cases of 'present contrary to fact' one should use the subjunctive. That means that in all such 'if' cases one must write 'were' and not 'was' (If I were, if you were, if he/she/it were...). True, you will often find the usage 'If ... was' (even among the Duolingo experts!), but grammarians still consider this incorrect, although it has become common in vernacular US English.
You're absolutely right, and I have always known that. But, with the general dumbing down of English, esp. by US influence (for example by not forming adverbs from adjectives, as in "you sang amazing" instead of "you sang amazingly" and other areas of laziness in grammar, spelling, and punctuation), I had assumed this was perhaps another instance of misuse that was becoming the norm. I'm all for preserving the full expressiveness of English even if others aren't sensitive to its subtleties.
so does this mean that when you are making a conditional, the structure like "zouden zijn" could be used in both part of the sentence? I mean in English usually it's like were+would be or had done+would have done, the "would" dont usually go to both part. by the way what should i say if i want to mean "i would have done"? thanks~
It's against English grammar. In proper English the first conditional sentence type is: IF + Present Simple + Future Tense (will); the second conditional sentence type: IF + Past Simple + Conditional (would); and the third conditional sentence type: IF + Past Perfect + Past Conditional.
Generally, the meaning might be the same, but it's important to translate words and phrases as precisely as the two languages allow. On another occasion, you might need to alter the meaning of "not possible" / "niet mogelijk" by turning it into something like "It is not only possible, but even desirable" / "Het is niet alleen mogelijk, maar zelfs gewenst", which you can't do with 'impossible' / 'onmogelijk'.
Strictly speaking not good English - it should be subjunctive - If there were no sun, life would be impossible - or - if there had been no sun life would have been impossible. So - is zou zijn subjunctive here, or can you have two conditionals in one sentence in Dutch? Not the case in English (or Italian, which I'm also studying.)