Which of the Following Is a Valid Comparison of Roman

Which of the following is a valid comparison of Roman and Han mining operations?

A) Rome and the Han both imported most of their iron ore from tributary states.
B) Rome exported far more bronze and copper tools than did the Han.
C) Roman and Han mines both polluted the environment, but Roman pollution was more extensive.
D) Rome used free conscript laborers in its mines, while the Han used slaves.