This focusing is the main reason that even relatively weak sounds in the ocean, especially low-frequency ones, can often travel thousands of miles.

正是由于这种集声，即使是海洋中相对微弱的声音，尤其是低频声音，也能传播数千英里。

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The main effect of these additional observations is a 100-point increase in the frequency count for each response alternative.

这些额外调查对象的主要影响是，使得每个回答情形的频率计数增加了 100 点。

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But some of those precious minutes would be saved by making fewer stops, while train frequency on the traditional west-coast main line will be cut.

但是，这几分钟的宝贵时间将通过减少停靠站的方式节省下来，而传统的西海岸主干线的列车班次会减少。

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The photovoltaic panels generate electricity when exposed to sunlight and are connected to the building's power supply via an inverter synchronised to the electricity main's frequency.

BBC: Solar power for City Works centre in Gloucester

There are two main methods of creating a single-frequency network.

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The sound of rocket fire has been getting louder in the town, while the frequency of ambulances and trucks bringing wounded to the main hospital has been increasing, AFP news agency reports.

BBC: Libya: Government and rebels still battling for Brega