The key remaining step is a comprehensive test of the entire system at sea, which is much more difficult than test flights over land.

剩下的关键步骤是一项整个系统在海面上的综合测试，难度远远大于在陆地上的飞行测试。

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Modern communication system is a land-sea-space three-dimensional communication network whose realization is mainly restrained by underwater communication.

现代通信系统是陆-海-空三维通信网，三维通信网的组成主要制约于水下通信。

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Shanghai has fostered a comprehensive transportation network that incorporates land, sea, and air travel, as well as a convenient urban transportation system.

上海已树立了一个综合的交通运输网络，包含陆，海，空交通，以及一个方便的城市交通系统。

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Safety is essential to any transportation system whether on land, sea or air, and space shuttles are a vivid example of that axiom.

FORBES: He Brought Safety To The Skies

The soundest experts in this field advise that we need to build a fully integrated system which combines both space- and sea-based components, rather than the fixed, land-based one favored by the present administration.

CENTERFORSECURITYPOLICY: Center For Security Policy