These layers and be added or removed dynamically and you can change each layer as it has a track that lets you change it as a function of time by inserting keys at certain frames in the track.

这些层可以被动态的增加或删除，你也可以对这些层进行改动，因为每层都有一个轨道，你可以在轨道中的特定时间点加入关键帧到达改变动画的目的。

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The UDP layer of the stack keeps track of the quantities of the writes and ensures that when the receiver on the right gets the data through the socket, it arrives in the same quantities.

协议栈的 UDP 层追踪写的数量，并确保当右边的接收者通过套接字获取数据时，它以同样数量的字节到达。

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NPP carries five science instruments designed to help researchers track everything from the ozone layer to ice cover, and to help them develop both long - and short-term forecasts.

NPP携带了5台科学仪器，用来帮助研究者跟踪从臭氧层到冰盖的各种信息，并协助他们开展长期和短期预测。

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