题目内容

Most people think of lions as strictly African beasts, but only because they"re been killed off almost everywhere else. Ten thousand years ago lions spanned vast sections of the globe. Now lions hold only a small fraction of their former habitat, and Asiatic lions, a subspecies that split from African lions perhaps 100,000 years ago, hang on to an almost impossibly small slice of their former territory.India is the proud steward of these 300 or so lions, which live primarily in a 560-square-mile sanctuary (保护区). It took me a year and a half to get a permit to explore the entire Gir Forest—and no time at all to see why these lions became symbols of royalty and greatness. A tiger will hide in the forest unseen, but a lion stands its ground, curious and unafraid lionhearted. Though they told me in subtle ways when I got too close, Gir"s lions allowed me unique glimpses into their lives during my three months in the forest. It"s odd to think that they are threatened by extinction; Gir has as many lions as it can hold—too many, in fact. With territory in short supply, lions move about near the boundary of the forest and even leave it altogether, often clashing with people. That"s one reason India is creating a second sanctuary. There are other pressing reasons, outbreaks of disease or natural disasters. In 1994 a serious disease killed more than a third of Africa"s Serengeti lions—a thousand animals—a fate that could easily happen to Gir"s cats. These lions are especially vulnerable to disease because they descend from as few as a dozen individuals. "If you do a DNA test, Asiatic lions actually look like identical twins," says Stephen O"Brien, a geneticist (基因学家) who has studied them. Yet the dangers are hidden, and you wouldn"t suspect them by watching these lords of the forest. The lions display vitality, and no small measure of charm.Though the gentle intimacy of play vanishes when it"s time to eat, meals in Gir are not necessarily frantic affairs. For a mother and her baby lion sharing a deer, or a young male eating an antelope (羚羊), there"s no need to fight for a cut of the kill. The animals they hunt for food are generally smaller in Gir than those in Africa, and hunting groups tend to be smaller as well. What impressed the author most when he went to watch the lions in the Gir Forest

A. Their friendliness.
B. Their size.
C. Their intimacy.
D. Their vitality.

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A. 抑制剂与酶的活性中心结合
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C. 增加底物浓度可解除抑制
D. 抑制程度与[S]和[I]有关

能使胰蛋白酶原激活的物质是

A. 肠激酶
B. 胰凝乳蛋白酶
C. 羧肽酶
D. 弹性蛋白酶

有关激活剂的叙述,恰当的是

A. Mg2+是多种激酶的激活剂
B. 辅助因子都是酶的激活剂
C. 可使酶由无活性变为有活性
D. 胆汁酸盐是某些酶的激活剂

pH影响酶促反应速率的原因是

A. 影响底物的解离
B. 影响活性中心结合基团的解离
C. 远离最适pH的酶发生变性
D. 影响活性中心催化基团的解离

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