Examples of using "улучшились" in a sentence and their english translations:
My grades have improved significantly.
And her cubs seem no closer to making a kill.
My grades have improved since first semester.
Her grades have improved significantly.
My son's ability at math has improved this year.
Thankfully, as the year went on, my language skills improved slightly,
I see that your manners haven't exactly improved in the last twenty years.
I think if I talked more often with a native speaker, my English skills would improve quickly.