@swth - re: "Tomorrow it is not Thursday."
Hola swth. You bring up a good point about duo not liking the pronoun 'it' added to your translation of this excerise sentence.
"Subject personal pronouns are usually omitted in both spoken and written language, as the grammatical person and number of the subject are explicit in the verb form. For this reason Spanish is considered a "pro-drop language". Nevertheless, subject pronouns can be used for emphasis or contrast, or to avoid ambiguity."
In the case of your translation, "Manzana" is the subject and is explicitly stated in the sentence.
Adding the third personal neuter pronoun 'it' is redundant and was not done in the root language sentence.
A user by the name of Lago is quick to point these types of errors out and I have adopted his philosophy. It works pretty good in duo.
In short, the idea is, "keep your transactions as close to the spiritual and literal meaning of the root sentence." :)
I think this makes things more complicated. Apart from not knowing what "spiritual meaning" means, "Tomorrow it's not Thursday" is a literal meaning of the root sentence. It is grammatically correct, and as such it should be accepted. With a note saying '"Tomorrow is Thursday" is more common.'
When you mouse over it looks like it could also mean "Morning is not especially difficult." I get that in this (well, lack of) context is means that tomorrow is not Thursday, but if the context was different (say a conversation about work during morning, midday and afternoon), could it also mean the other thing?