Among the dead in South Asia's tsunami① were many tourists at Sri Lanka's national wildlife park at Yala. But very few of the park's animals - elephants， buffaloes， monkeys and wild cats - appear to have died. There are theories that animals can sense natural disasters and flee to safety.

First， it's possible that the animals may have heard the quake before the tsunami hit. The underwater rupture likely produced sound waves known as infrasound② or infrasonic sound. Humans can't hear infrasound， but many animals including dogs， elephants， tigers and pigeons can. A second early warning sign the animals might have sensed is ground vibration③。 The massive quake would have produced vibrational waves known as Rayleigh waves. These vibrations move through the ground like waves move on the surface of the ocean but faster. They travel at ten times the speed of sound. The Rayleigh waves would have reached SriLanka hours before the water hit. Mammals④， birds， insects and spiders can sense Rayleigh waves. So the animals at Yale might have felt the Rayleigh waves and then run to higher ground. But what about humans？ While we can't hear infrasound， we can feel it， although we don't necessarily know we're feeling it. We also experience Rayleigh waves by special sensors in our joints⑤， which exist just for that purpose. Sadly， it seems we don't pay attention to the information when we get it. Maybe we screen it out because there's so much going on before our eyes and in our ears. Humans have a lot of things on our minds and usually that works out OK.

Vocabulary:

   ① tsunami  n. 海啸

    ② infrasound  n. 次声

③ vibration  n. 振动，颤动

④mammals  n.哺乳动物

⑤joint    n.关节

Choose the best answers according to the above：

  1. Why did few animals at Yala die when the tsunamis that caused a huge number of human deaths hit？

    A. Because the animals were staying at a higher place in the park.

    B. Because the animals were able to run much faster than human beings.

    C. Because human beings cannot hear the infrasonic sound.

    D. Because the animals might have picked up the danger signals and ran away.

    2. Which of the statements about "Ravleigh waves" is true？

A. Rayleigh waves are massive vibrational waves that usually cause quakes or tsunamis.

    B. Rayleigh waves move on the ocean surface at a speed ten times that of sound waves.

    C. Rayleigh waves can be felt both by animals and human beings.

    D. Rayleigh waves， just like infrasonic sound， can only be felt by animals.

   3. When a tsunami hits， it is possible that ＿＿＿＿

    A. we can't feel the infrasound so we can't be informed of the danger

    B. we can feel Rayleigh waves as well as infrasound so we are able to escape the danger like animals

    C. we were so busy with things on our minds that we feel neither infrasound nor Rayleigh waves

    D. we think nothing of the information of its coming even though we can also get it

4. What does the underlined word "that" in the last sentence refer to？

    A. Screening out the information.

    B. There being so much going on before our eyes and in our ears.

    C. Having a lot of things on our minds.

   D. Paying attention to the information.

KEYS:

1. D  细节理解题。从第二、三段可知，动物能提前感知到危险临近，逃到安全地方去

2. C  细节理解题。从第三、四段可知，人和动物都能感觉到Rayleigh waves.

3. D  细节理解题。从最后一段第四句可知。

4. A  词义猜测题。该词指代的意思从前一句Maybe we screen it out because …可以确定。

Background Information:

动物为什么会预报灾难？科学上有以下几点解释和推测：

 第一，对超声波和次声波的感受。鱼类和其他一些水生动物能感受到人所不能感受到的超声波和次声波。一般人所能感受到的声波范围为16 Hz~20 000 Hz，小孩可以达到 22 000 Hz，高于或低于这个声波范围就不能感受到。鱼类内耳和身体两侧有侧线感受器，这是一种机械感受器，能感受1~25 Hz的次声波，即使对水流压力的微小变化或微弱的水流波动也很敏感；水母（海蛰）的伞体边缘有感觉球，能感受8~13 Hz的次声波。漂浮在海面的水母，能在暴风到来之前，感受到由于流动空气与波浪摩擦而产生的次声波，因此及时离开浅海，避免了被巨浪砸碎的灾难；在海洋中的海豚，能感受到50~100 000 Hz的声波，又具有完善的声纳系统。因此，它能利用超声波和次声波正确地追踪千米以外的鱼群，并能分辨出种类。由此可见，鱼类和其他一些水生动物在震前出现异常反应的原因，很可能是与强震前有超声波和次声波发生有关。此外，蝙蝠能感受1 500~150 000 Hz 的声波。它的超声定位系统极为优越，不仅分辨率高，而且抗干扰性强，能从比信号高出200倍的噪声背景中接受小昆虫身上反射回来的信号。因此，蝙蝠在地震前迁飞，是与感受超声有关的。

  第二，对热的变化的高度敏感。在地震前，穴居动物都有明显的反应。例如，蛇类具有颊窝或感觉小窝，窝内的感觉细胞对“热”极为敏感。有人用南美洲的蟒蛇做过实验，在波长为10 600 nm的红外线下热量在0.084 J/cm2时，就有热感觉反应。由此推测，蛇在震前的异常反应，可能与地热变化有关。

  第三，对微弱的机械振动的感受。家禽和鸟类的腿部具有微小的感震体，它们凭此能感受到枝头或地面上十分微弱的机械振动（几十至上千赫）。中国科学院生物物理研究所曾做过这样的实验：把100只家鸽分作两组，每只50组，将其中一组家鸽的感振小体和中枢神经之间相联系的神经切断。结果，在一次4级多的地震前，被切断神经的一组基本上安静如常，而另一组家鸽都惊飞了。这说明家鸽的感震小体能感受到震动的波动。在强震前，猪、牛、羊等家畜普遍出现异常反应的原因，可能与它们的腿部、趾部和腹部肠系膜等部位，分布着大量对机械振动非常敏感的环层小体有关。

  第四，对海水压力的感受。在海啸到来之前，往往会有一些深海鱼类因受不了深海地震而引起的水温骤升而逃命，因为这些深海鱼类所处的生活环境，其水温终年在0oc~ 2oc。由于温度的剧变，无形中给深海鱼类巨大的打击，即使这些深海鱼类逃到水面上，也是死路一条。因为深海鱼类平时一直承受着海水的巨大压力（水深每增加10 m就会增加101.3 kpa的压力），如果突然到了水面上，由于海水的压力骤然减小，会使它们的胃翻出口外，眼睛突出眼眶外，体内部分小血管破裂，最终导致死亡。因此，在浅海中游玩的人们，一旦看到一些怪模怪样已经死去的深海鱼类，就应当引起高度警觉，万万不可掉以轻心，这说明有可能过不了多长时间，凶猛的海啸就会疯狂席卷过来，在这里游玩的人们将会被无情的海啸吞噬掉。因此，防患于未然是十分必要的。