(A) During his research on modern production systems, workers at a leading automobile manufacturing firm told Professor Roberts that these systems end up encouraging temporary or contract employment and reducing their quality of life.
Wrong because pronoun "his" cannot be used for workers.(B) Modern production systems were encouraging temporary or contract employment and reducing their quality of life was told to Professor Roberts by the workers at a leading automobile manufacturing firm.
Wrong because told to is incorrect usage.(C) Professor Roberts was told by workers at a leading automobile manufacturing firm that these systems ended up encouraging temporary or contract employment and reducing their quality of life, during his research on modern production systems.
Wrong because modifier during his research on modern production systems should come after Professor Roberts.(D) During his research on modern production systems, Professor Roberts was told by workers at a leading automobile manufacturing firm that they were meant to encourage temporary or contract employment at the same time reducing their quality of life.
Wrong because it is not clear as to what "they" refers to.(E) Professor Roberts, during his research on modern production systems, was told by workers at a leading automobile manufacturing firm that these systems ended up encouraging temporary or contract employment and reducing their quality of life.