两个月交一次作业：北极圈的海底

Gleaming starkly white, the frozen Arctic Ocean crowns the top of the world above 66 degrees north latitude.

In the Arctic, above the ice and below, wildlife prospers in what might seem to be an inhospitable environment.

But it's exactly what is required for polar bears, ring seals, and the snowy-white beluga whales -- the highly vocal canaries of the sea.

Narwhals, the legendary unicorns of the sea, and bowheads, the great ice whales, thrive there and nowhere else on Earth.

In the cold, dark waters of the Arctic, life abounds as it has for millions of years.

学习资料来源：大耳朵
The real beluga and narwhals' singing audio borrowed from:
http://www.dosits.org/gallery/intro.htm

There is a slip in my read, but i'm too lazy to correct it...Sorry about this~~_:$ _:$