151 篇文章
It's an event that only happens once or twice a year at the most.
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It's an event that only happens once or twice a year at the most. 而且一年最多也只发生1~2次

that for most of the year they would be unable to cross it.
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that for most of the year they would be unable to cross it. 它们一年中大部分时间都无法穿越这里

Each year explorers chart over a hundred miles of new cave passages.
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Each year explorers chart over a hundred miles of new cave passages. 每年 探险家们都会测绘 上百英里新的洞穴通道

as each year rainwater eats away a little more limestone.
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as each year rainwater eats away a little more limestone. 因为每年雨水都会侵蚀掉少许石灰岩

Every year almost 2 thousand million tonnes of sediment
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Every year almost 2 thousand million tonnes of sediment 每年大约有20亿吨泥沙在此沉淀

The Amazon transports a billion tonnes of sediment a year,
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The Amazon transports a billion tonnes of sediment a year, 亚马逊河每年会带来10亿吨的泥沙

For five months of the year it's sealed by an ice sheet over a metre thick.
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For five months of the year it's sealed by an ice sheet over a metre thick. 每年中总有5个月 湖面被1米厚的冰层覆盖

Each year nearly two million animals migrate across the Serengeti plains
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Each year nearly two million animals migrate across the Serengeti plains 每年都会有将近200万只角马 横越塞伦盖蒂平原

but every year some of the world's high rivers are crowded by millions of visitors.
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but every year some of the world's high rivers are crowded by millions of visitors. 而世界上的高山河流每年都将 迎接成千上万的来访者

There is a tropical downpour here almost every day of the year.
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There is a tropical downpour here almost every day of the year. 这里全年几乎每天都会降下热带暴雨