To my understanding, im Juli means in "that" month July, so we don't say in Juli without that article. It seems von monat zu monat is a fixed expression. So if we don't use definite article for monat, we won't use that for a specific month. http://www.linguee.de/deutsch-englisch/uebersetzung/von+monat+zu+monat.html
The preposition of im or expanded in dem (der case dative) is use to answer a question where to go/do? But if use in den (der case akkusativ) is to answer the question of where is?
So taking that think vom(von dem) is like to say where is september going? Ahhh goes to after of august, then you say august bevor vom september, while von (vor den) is use where is the september? Ahh this is in a period of this and this where september is into , is included, so we use von and can w say wir sind neu von september, also people makes your homework
Frankly, there are a lot of things wrong with this. First, of all, you're mixing up accusative and dative. "Im" is used for where something takes place, and "in den" for where someone/thing is going. Secondly, that only works for two-way prepositions like in, auf, unter, hinter, neben, and über. Von is a dative preposition; it never takes accusative. The only time you'd see "von den" is in dative plural. Thirdly, vor has nothing to do with von.
Rule of thumb:
- if there's an L, then the ending is -lich
- if there is no L, then the ending is -ig
I don't think -ich by itself is an ending, just as part of -lich (which is connected to English -like and -ly).
Meanwhile, -ig is connected to English -y (e.g. haarig "hairy").
"Jährlich vom Juni bis zum August" is also correct but not "in Juni". After the word "und" is a second "im" not necessary: "im Juni und (im) August. It can be: "von Monat zu Monat" or "von einem Monat zum anderen (Monat). And two exemples to "zwischen": 1. Diese Pflanze blüht (is in bloom) zwischen Juni und August (generally). 2. Er kommt irgendwann zwischen dem 20. Juni und dem 8. August.
It would sound odd to me, but I'm not sure whether it's wrong per se.
But if you have a start and an end, then "von ... bis ..." sounds most natural to me.
A bit like how you can say "starting in April" in English, but at least for me, "starting in April till November" sounds odd, if not completely wrong.
You can't really translate words 1:1, but that's one of their uses, when referring to time.
You use von A bis B when describing a bounded time period, and ab C when describing an open-ended time period with a start but no explicit end. (and bis D when describing an open-ended time period with an end but no explicit start.)
Good example of Duo failing to construct reasonable examples. My ear is listening for a subject and hears "Er" or "Ihr" then there is a verb that sounds like "licht" then we have from "Uni" and I am thinking about something a university student does.
By using random fragments rather than coherent sentences that give clues as to context, Duo actually damages the process of comprehension. In conversation you would not be left high and dry like this.