What Became a Major Problem in the Lowell Mills by the Middle

What became a major problem in the Lowell mills by the middle 1830s?

A) a shortage in cotton and other materials needed to create cloth
B) the growing dominance of textile mills in the South
C) the long commute of workers from out of state
D) labor unrest due to working and living conditions
E) their reliance on the work of enslaved Africans