已知a²+3ab+b²=0（a≠0，b≠0），则代数式 $\frac{a^2+b^2}{ab}$ 的值等于____．

    After two years of careful consideration, Robert McCrum has reached a conclusion on his selection of the 100 greatest novels written in English. Take a look at a few in his list:

    The Pilgrim's Progress by John Banyan (1678)

    A story of a man in search of truth told with the simple clarity and beauty of Bunyan's prose makes this an English classic.

    Robinson Crusoe by Daniel Defoe (1719)

    By the end of the 19th century, no book in English literary history had enjoyed more editions and translations. This world-famous novel is a complex literature that one cannot resist.

    Gulliver's Travels by Jonathan Swift (1726)

    A great work that's been repeatedly printed, Jonathan Swift's Gulliver's Travels comes third in our list of the best novels written in English.

    Clarissa by Samuel Richardson (1748)

    Clarissa is a tragic heroine, pressured by her dishonorable family to marry a wealthy man she dislikes, in the book that Samuel Johnson described as “the first book in the world that shows the knowledge about the human heart”.

    Tom Jones by Henry Fielding (1749)

    Tom Jones is a classic English novel that gets the spirit of its age and whose characters are well-known since they have come to represent the society at that time.

    Emma by Jane Austen (1816)

    Jane Austen's Emma is her most outstanding work, mixing the best parts of her early books with a deep sense of feelings.

    The Narrative of Arthur Gordon Pym of Nantucket by Edgar Allan Poe (1838)

    Edgar Allan Poe's only novel—a classic adventure story with supernatural elements—has fascinated and influenced generations of writers.

581年，夺取北周政权，建立隋朝的是（　　）

冬眠的奥秘

张劲硕

    ①严寒的冬天，我们总是向往着在被窝里长眠一冬——能像狗熊和青蛙那样冬眠就好了。然而我们大都不知道：那些冬眠的动物们，掌握着我们人类尚不知晓的惊天奥秘。

    ②冬眠是动物应对恶劣环境的一种策略，科学上叫“蛰伏”。有人会问，冬天里睡得多、睡得久，不就是冬眠吗？它们还真不是一回事儿，只是二者的区别不太容易看出来。拿鱼来说，有几类鱼是会冬眠的，包括我们熟悉的鲤鱼、乌鳢，还有海里的鳗鲡。每当冬天来临，它们就把自己调到冬眠档：不吃、不喝、不游动。这看似与正常档的睡觉并无二致，但请注意它们的鳃！鱼类靠鳃呼吸，平时就算身体静止不动，鳃也会轻轻开合扇动。而进入冬眠的鱼，鳃也几乎不动，完全处于麻痹状态。除了呼吸，冬眠动物的体温、心跳等生命指征也都降到极低的水平，新陈代谢速率变得非常缓慢，与休克和死亡标准只差那么一点点——这就是冬眠与睡觉的本质区别。

    ③冬眠的意义在于，尽量减少身体内外的生命活动，将能量消耗降到最低，以挨过环境严酷的时间段。动物冬眠时，能把生命的时钟调得极慢。比如生活在北美洲的普通箱龟，冬眠时心脏5--10分钟才跳1次，实在让人惊叹。更夸张的是，它们几乎完全不呼吸，只靠皮肤吸入少许氧气！

    ④科学家还发现，冬眠不是“习惯养成”的问题，而是遗传基因决定的“天赋”。这种“天赋”还与寿命的长短有联系。一般来讲，哺乳动物的寿命与体型相关，体型小的新陈代谢快，寿命短；体型大的新陈代谢慢，寿命长。比如大象就活80年，兔子七八岁就算高寿。而蝙蝠打破了这个规律——冬眠的菊头蝠和同体型的、不冬眠的老鼠相比，前者可以活到30多岁，后者却只有3、4岁。如果在同一物种中比较，如蝙蝠或者棕熊，依然是冬眠的寿命要长很多。

    ⑤冬眠是当下的热门研究领域。如果人类能像动物们一样冬眠，收获的就绝不仅仅是睡大觉的幸福感，也许还能长生不老。虽然对蝙蝠和棕熊等冬眠动物的研究能确定冬眠基因与长寿有关。但这些动物毕竟与我们人类相差太远。不过，在2004年，有个轰动科学界的发现：居然有一种猴子能冬眠！而人类跟猴子同属灵长类动物，基因相似性很高。如果猴子能冬眠，这意味着我们人类也有可能做到。到那时，我们的寿命说不定可以达到800岁！

（选自《博物》总第146期，有删减）