TOEFL Listening: ETS-TOEFL听力机经 - 5YR1DTE43YLFN95KP$

According to the professor, what are two problems with using pumice stones to fade jeans? A. It is hazardous to the people who work with it. B. It contributes to waste-water pollution. C. It causes excessive damage to the items it is used on. D. It needs to be combined with other processes to be effective.