What was not examined by the investigative journalists in the late nineteenth and early twentieth centuries?
A. Brutal working conditions in mines on railroads
B. long hours required of sharecropping farmers
C. John D. Rockefeller’s corrupt practices at standard oil
D. Violations in the meatpacking industry

A

Explanation:

C and D are easily eliminated; farmer life did not grow. It's been steadily shrinking since the 1700s. B sounds good initially, but people were moving to cities, where all the attainable jobs and payable rents were - most people couldn't afford to just buy a ton of land and start farming, and suburbs didn't really exist for the same reason. So it has to be ‘A’.

the answer is "by providing data about careers and annual mean wages"