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。
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.
但是，在决定关闭机场时并未考虑何为危险、隐性伤害和安全间的界限以及这三种级别如何随火山灰微粒类型与数量的变化而改变的因素。
But where the boundaries between danger, potential damage and safety lie, and how they vary with the type and number of ash particles, was not taken into account in the decisions to close airspace.
柏林墙的倒塌带来了新的希望，但是这种紧密接触也带来了新的危险—这些危险不受国界限制或大洋阻隔。
The fall of the Berlin Wall brought new hope. But that very closeness has given rise to new dangers-dangers that cannot be contained within the borders of a country or by the distance of an ocean.
应用推荐