一旦语言从2岁左右开始发展，他们就有了一个符号表征系统，可以谈论过去和现在环境之外的事情。

Once language starts to develop from about age 2, they do have a system for symbolic representation and can talk about things which aren't in their immediate environment including the past.

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群时延是系统和网络的一项重要传输特性，它表征系统和网络的线性失真。

The group delay, which characterizes the linear distortion of the system and network, is an important transmission characteristic.

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这两个问题重构相空间受到强烈的噪声干扰，而无法用来表征系统的混沌特征。

These two problems make the phase space reconstructed suffer a heavy noise disturbance so that it can not be applied to characterize the chaotic system.

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