听力原文： Dr. Williams in New York carried out a study of cats, which had fallen out of windows of apartment blocks. Nine out of ten survived a fall of two storeys or more. One cat fell from a flat on the thirty- second floor and only lost a tooth. Interestingly, the cats were most at risk from injury or death if they fell from the seventh floor. Falling from either a lesser or greater height gave them a better chance of survival.
What is the significance of the seventh floor？ The study shows that this is the distance cats take to reach their terminal speed, i.e., the final speed that does not change once it is reached. After the seventh floor, it may be that they relax and spread out their legs like a flying squirrel. This would slow them down and allow their muscles to absorb more of the force of impact, which would reduce the damage.
Cats also have a very well-developed sense of balance. They can change position while falling so that they land on their feet. This has the advantage of spreading the force of impact with the ground over four legs and so does less damage to each leg.
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A. Nine out of ten.
B. One third.
C. Elven out of thirty.
D. One fourth.