（）是战国时在楚国民歌的基础上形成并流行的一种歌曲体裁，实际上也是我国古代南方音乐文化的代表。

Why does the Earth show almost no signs of having been hit by numerous meteors in the past

A．Humans have built over most of the craters.

B．Most meteors fell into the ocean and not on land.

C．The Earth's magnetic field repelled most meteors.

D．The Earth's natural geologic activity has eliminated most traces.