Answer:
B. to explain how Phillis became an accomplished writer
Step-by-step explanation:
John Wheatley's letter to the publisher of Phillis Wheatley's poems was to explain how Phillis became an accomplished writer.
His letter was descriptive of how far Phillis had come as a writer, how she learned English, a foreign language, and how she became proficient in writing at such a short time.
Below is an excerpt of the letter:
"...without any assistance from school education, and by only what she was taught in the family, she, in eighteen months’ time from her arrival, attained the English language, to which she was an utter stranger before, to such a degree as to read any..."