VOA慢速英语:NASA: Strong Evidence of Liquid Water on Mars

短语讲解：

1. In March, NASA said there was once more water on Mars than in Earth's Arctic Ocean.

once more 再一次,又一次
例句：At this moment, in this election, we must pledge once more to march into the future.
在这一时刻，在这次选举中，我们必须再一次保证，向未来挺进。

2. They say more than four billion years ago, Mars was covered with water 137 meters deep.

more than 多于，不仅仅
例句：More than two students have been concerned in this affair.
这件事情牵涉到两个以上的学生。