单项选择题

The question which is discussed in the passage is

A.how historians should explain the origins of the conditions in the Chicago meat-packing industry,
B.why it is difficult to determine the actual nature of the conditions in the Chicago meat- packing industry.
C.why a particular account of the conditions in the Chicago meat-packing industry is inaccurate.
D.what should be included in any account of the Chicago meat-packers’ role in the national labor movement.