The Northern Cities Vowel Shift and Speakers That Adopt It

The Northern Cities Vowel Shift and Speakers That Adopt It
"The Northern Cities Vowel Shift" is not adopted by all speakers that live in the geographic regions where it is in progress. Studies (1) illustrate that it is mostly European Americans who show evidence of taking on the shift; however, there is little to no research indicating that speakers of African American Vernacular English employ the shift in their speech. Canadians that share proximity to the Great Lakes with speakers that live in the United States also show no evidence of adopting the shift.
This shift, also called "The Northern Cities Shift" (NCS) , is a (2) linguistic phenomenon that occurs in the northern geographic area of the United States known as the Inland North, which includes such cities as Rochester, Buffalo, Detroit, and Chicago. Although prominent among some urban inhabitants of the region, NCS is not considered the standard. (3) Linguists describe one change that occurs in speakers of NCS in which the vowel in milk (4) "shifts" down and back (the tongue is lowered and travels back) from a short "i" to a short "e" that could be represented as melk.
William Labov, a professor at the University of Pennsylvania, is one of the largest contributors to research on the subject of the NCS. His theory is that the shift possibly started when speakers from different (5) language varieties were brought together in the early 1800's when the Erie Canal was being constructed. People from the East Coast moved to the Great Lakes region, and their dialects mixed resulting in an ongoing shift. However, not all speakers of the Great Lakes region participate in this linguistic variation.
In paragraph 1, why does the author include the information that African Americans do not participate in the NCS?

A) To explain why African Americans do not say "melk" instead of "milk".
B) To support the claim that African Americans in the Great Lakes region do not participate in the NCS.
C) To provide evidence that not all speakers in the Great Lakes region adopt the NCS.
D) To show that there is little to no research that African Americans take on the NCS.