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1.date 确定年代
The skeleton has been dated at about 2000 BC.
这骨架的年代为公元前2000年左右。
2.descendant 后代
These adaptations served their descendant well as they invaded land.
这些适应机制在它们的后代进化成陆生生物时起了很好的协助作用。
3.upper limit 上限
Remember: there is no official upper limit to how much a person can spend in a lifetime.
记住，一个人一生能花多少钱，没有官方上限。
4.a set of 一组
Most genes are regulated by a master set of genes.
大多数基因都是由一组主基因来调控的。
