Answer:
The correct answer is C. progressed.
Step-by-step explanation:
The underlined word, improved, means to get better. Progressed is a synonym of improved, which means that they mean similar thing.
The other thing is that the other words can easily be considered synonyms to progressed, but they don't make sense in this particular sentence.
Therefore, the correct answer is C. progressed.
Hope this helps! :D