So it's no wonder that his sudden death on Saturday, at the tender age of 4, has sent a nation into mourning — and sparked a controversial debate on the ethics of keeping polar bears in captivity.

因此，当年仅4岁的他在周六突然死亡时，就不难理解德国上下的一片悲伤和由此引发的关于圈养北极熊的激烈讨论了。

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"I wrote this book for dolphins because we are mistreating these animals by keeping them in captivity," Brenner said.

我写这本书是为了拯救海豚。因为我们人类正通过拘囿的方式来虐待这些生灵。

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Millionaire Zhou Weisen, who is 47 and was born in the Year of the Tiger himself, realised at an early age he could make his fortune by keeping tigers in wretched captivity.

百万富翁Zhou Weisen【周伟森】，他自己就是在四七年虎年出生，早年他就意识到可以通过圈养老虎来牟取财富。

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And if a zoo is treating the bear well - as he believes Berlin Zoo was with Knut - then keeping some in captivity is a price worth paying.

BBC: Knut: A polar bear story

Many animal welfare organisations argue that the capturing and keeping of dolphins in captivity is cruel.

BBC: Dolphins helped my child

Blackfish, about the consequences of keeping killer whales in captivity, is among the documentaries that will be screened at the O2's Cineworld cinema multiplex between 25 and 28 April.

BBC: Sundance London film festival announces 2013 line-up