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. Mammals, 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 joints, 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.
Notes:
① tsunami n. 海啸
② infrasound n. 次声
③ vibration n. 振动，颤动
Choose the best answers according to the above:
小题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.小题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.小题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小题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.
