"She becomes quiet."
Translation:Cô ấy trở nên yên lặng.
I have learned before that tro thanh is used for nouns and tro nen for adjectives.
Not much, they're practically the same thing although if you single out the second syllables you get the words nên (to ought to) and thành (to become).
I wrote "Cô ấy trờ nên yên tĩnh" but my answer wasn't accepted...my Vietnamese friend told me this was fine. Are they wrong?