Alguém poderia me explicar o uso da partícula の e do と nessa frase?

Question

日本の学生の多くは、18歳になるとこれまでの環境と大きく変わります。

Eu percebi que tem alguns substantivos que precisam ser usados juntamente com o の na frase, mas as vezes não sei se é preciso ser antes ou depois. Por exemplo, 環境の ou の環境. E no caso do と, eu acho que está sendo usado por causa do 変わります.

English (courtesy of Google Translate)

I noticed that there are some nouns that need to be used together with the の in the sentence, but sometimes I don't know if it needs to be before or after. For example, 環境の or の環境. And in the case of と, I think it's being used because of 変わります.

Answer 1

日本の学生の多くは、18歳になるとこれまでの環境と大きく変わります。
For most Japanese students, when they turn eighteen, the environment (they have lived in) up until now changes a lot

これまでの環境 means "the environment up until now". In XのY, X describes Y. The sentence should still make sense if you remove Xの. For example, removing これまでの gives: ...18歳になると環境と大きく変わります "... when they turn eighteen the environment changes a lot", but removing の環境 gives a meaningless sentence: ".. when they turn eighteen the up until now changes a lot".

I'm surprised you asked about これまでの環境. For me the more confusing part is 日本の学生の多く. I'm a little unsure here so some confirmation from a more experienced speaker would be useful. I think 日本の学生の多く and 多くの日本の学生 are both valid. 多くの日本の学生 Would mean "many Japanese students" and we can certainly remove 多くの and leave a valid sentence: "Japanese students, when they turn 18 ...". With 日本の学生の多く I think it better translates as "most Japanese students" and again I could remove 日本の学生の to get "Most, when they turn 18 ...", though there would have to be previous context for you to know who 'most' was referring to.

Finally, the と in これまでの環境と大きく変わります. The stripped down sentence would be 環境と変わります. This と is a particle marking a comparison. It is comparing これまでの環境 (the environment up until now) with an inferred new environment and saying that there is a change. Perhaps this post explains it better than I can.

Edit

Note that the translations offered above are rather loose. As discussed in the comments the subject of 変わります should be the environment of the student before they turn 18, but this is omitted from the sentence. To be clear, the phrase marked with と is the thing that is being compared against and not the thing that changes. The full structure should be XがYと変わります -- X changes compared to Y. But Xが (the previous environment) has been omitted. This makes the original sentence rather clunky.