"diction" means word choice, aka the words that one chooses when writing or speaking. choice A uses this word correctly, because if you know more words, you'll be able to use "good diction" aka you'll have more words to choose from.
It is option A because of the meaning of ''diction'' and knowing the meaning of diction if we try fitting it into other sentences it will not match so we can conclude that it is option A because of the meaning of diction and because the meaning of diction helps us to understand that it can't fit with other sentences. And also because I took the test.
