the ice beneath the bears' feet starts to break up and then melt.北極熊腳下的冰層開始分裂融化

break up:破碎, 解散

The Government has broken up the large private estates.

政府把大片的私人地產分割開。

The ice began to break up on the river.

河上的冰開始碎開。

because they can't survive for as long without feeding as their mother.因為如果像母親那樣長時間不進食它們就無法生存

as long as:和 ... 一樣長

This line is four times as long as that one.

這條線是那條線的四倍長。

It's now summer and these bears have a choice-take their chances on the shrinking ice floes,
現在處于夏季北極熊們有兩種選擇，前往正在消融的浮冰上冒險覓食

take chance:冒險

You should never take chances when driving a car.

開車時決不應冒險。

We mustn't take chances,we'd better play safe.

我們不能冒險，我們最好來穩當的。