I'm agree with Android. I'm a native Russian and even sometime I was learning Ancient Russian, but for me, it's too difficult to explain. You need a teacher stronger than me to explain it well. I will try to explain this rule in my understanding. 'E' turns into 'ё' when an unstressed 'e' becomes a stressed (веснА singular - вЁсны plural, веслО singular - вЁсла plural). And it is encountered not only in plural (e.g. тЕтерев masculine - тетЁрка feminine; пятернЯ colloquial a palm, five fingers - пятЁрка five, a school mark "a"; медОк diminutive form - мЁд full; селО a big village with a church in feminine - посЁлок a village in masculine. I can't come up with any opposite examples yet, but I suspect they exist. E.g. мел - мелОк, although honestly here, 'e' has already been stressed as 'e' in the full form of the word. Just keep in mind: "e" goes into "ё" when it was unstressed and became stressed but it seems to me this is not an absolute rule. And remember 'e' can be stressed, can be unstressed; 'ё' can be only stressed. Sorry for my English.
Guys, if you want to ask me about something, come on.
Interesting idea, but I don't think so. Neither does Wiktionary: - https://en.wiktionary.org/wiki/azure#Etymology - https://en.wiktionary.org/wiki/%D0%BE%D0%B7%D0%B5%D1%80%D0%BE#Etymology
In a moment of inattention I answered эти озеры, and DL said that was just a typo... I'd like a report button that says "My answer is incorrect". )))
Seriously, when I have a typo or I just like DL's translation better, I'd like the option to do the question again, just as though I got it wrong. I'm finding some of my mistakes are persistent, and if I don't practise getting them right I won't. (Of course, what I do now is to write them 3 times in a text window, then again at the end of the lesson.)
"Эти" is the demonstrative pronoun for plural nouns. If you want to say 'these are lakes', you have to use "это". "Это" translates to 'this is'/'these are' and it is also a demonstrative pronoun for singular neuter nouns. Check out this guide if you want more clarifications/examples of using "это".