If an employee notices that a bucket with sanitizing water is becoming dirt, he/she should a) add more water to the bucket b) add more sanitizer to the bucket c) change the water and make fresh sanitizer d) grt clean towels to use

This is pretty much a "common sense" question.  It'd be best to get rid of the dirty sanitizing water and start fresh; in other words, he should change (throw out) the dirty water and make a fresh sanitizer.

By the way, this is the Math section; next time, please choose a different section more suited to your questions.