When we are looking at the life of a tree, we learn about that each period of life brings its own form of joy and challenge.

当我们观察一棵树的生命时，我们了解到生命的每一个阶段都有它自己的欢乐和挑战。

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FDA can ask for the proof of safety and effectiveness of a product if its distributors challenge FDA's authority.

如果经销商对FDA的权威提出质疑，FDA可以要求他们提供产品安全性和有效性的证明。

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However, additionality remains a challenge due to its inherent subjective nature.

然而，由于其固有的主观性质，额外性仍然是一个挑战。

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"A normal baby could respond to that challenge, lift its head up, turn its head and arouse or wake up,"

VOA: standard.2010.02.08

His remarks came a week after a federal appeals court said Aereo could continue its service despite a legal challenge by broadcasters.

WSJ: Exec threatens to pull Fox signal if Aereo goes on

In November, DARPA put street-level robots to the test in its Urban Challenge, a race of 12 autonomous cars through simulated city streets populated by obstacle cars.

FORBES: War Without Soldiers

The Company is providing open access to this data as part of its PacX Challenge, a global competition seeking new ocean applications and research using the PacX data set.

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