Much more is known about chemicals and cancer today than just 20 years ago, yet uncertainty about the risk of borderline carcinogens continues to hamper decisions.

• 今天人们对化学药剂和癌症的了解已比20年前增加了很多。可是，由于对致癌物的危险界限仍搞不清楚，这就妨碍了作出决定。