why not C understanding? Why could we make the leap from 1 competence to mastery?

he went from being competent to another level.

Competence already implies a certain level of understanding but then he elevated to the next level. From just average to skillful

he went to show great mastery.......................

So B is the correct choice
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OE


B The first clause in this sentence describes the playwright as “competent” in his first play, while the second clause asserts that he has progressed beyond mere competence in his second. Skill is an excellent prediction. Choice (B) mastery fits perfectly; the playwright no longer is merely competent, but is now masterful. You can reject (E) insufficiency as the opposite of what the sentence needs. Choices (A) characterization, (C) understanding, and (D) perception are all elements of writing that the playwright may have improved upon, but you’re looking for a more general word. Nothing in the sentence leads logically to a specific area of improvement.
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