Read the short text and complete the gaps with the appropriate prepositions, then mark the right alternative.

Perms and hair dyes linked to concerning compounds In a new study, hairdressers who often used light colored hair dyes or hair-waving products

(1) _____ clients had more potentially cancer-causing compounds

(2) ____ their blood than hairdressers who used the chemicals less frequently. The study included hairdressers as well as women who used hair dyes on themselves and some who had never used them at all, and none of the women had actually been diagnosed with cancer. The World Health Organization considers hairdressing work probably carcinogenic, since hairdressers tend to be

(3) ____ higher risk for bladder cancer. The new results could help narrow down specifically where the cancer-causing agents are coming from.