Just found that in Lesson 12, there are "Na" and "Nan". Both of them can mean "with". What is the difference between them? If "Na" is more of possessing something as you said above in April, what is "Nan" then? In your note, "nan" is "with/possessing/including"... which sounds the same to me as "Na"! Could you please explain it more?
Na has a bit of a tortuous history. In Ai na vedui Dúnadan! it means 'at' - Ah at last Dúnadan!. But, in the Etymologies (page 374 if you want to look it up) it's listed as both: Na = to, towards, at Na = with, by (takes the form Nan before vowels)
We find the second in some place names, such as Orod na Thôn = Mount of the Pine trees (literally 'Mountain with pines'). We know it's not 'to' as that wouldn't make sense. Context is everything for using 'na'.
Which, as I write this, I realise I haven't made clear at all in the lessons. I do apologise for that, and shall edit that lesson asap! (It's one of the first lessons I ever wrote, so it's what, three, four years old? I've done a lot of work since then).
Edit - I've updated the lesson, including how Anin can change if you're Gondorian.
Thank you very much for your detailed explanation. There is no need for apology, REALLY! I just think that more questions I ask you, more in details I can understand the beautiful language, and so I have kind of flooded your forum with my name. Others might have the same questions too!
Making up learning materials for such a complicated yet beautiful language is not easy. I have seen Sindarin learning materials from other sites and they don't seem to me to be as easy to understand as yours. So, gradually I just stick to yours and go do the exercises from another site (a.k.a. CoE) from time to time... and you know what? Xandarien... I do find it better and easier to just do the latter exercises over there with your materials!
Glad to hear that my questions/exercise(s) can give you ideas to improve your learning materials which will help others as well.