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cution, the righting of a tumbling
cat resembles a magician's trick. The gyrations of the cat in
midair are too fast for the human eye to follow, so the process
is obscured. Either the eye must be speeded up, or the cat's
fall slowed down for the phenomenon to be observed. A century
ago the former was accomplished by means of high-speed
photography using equipment now available in any pharmacy.
But in the nineteenth century the capture on film of a falling
cat constituted a scientific experiment.
The experiment was described in a paper presented to the
Paris Academy in 1894. Two sequences of twenty photographs
each, one from the side and one from behind, show awhite cat in the act of righting itself. Grainy and quaint
though they are, the photos show that the cat was dropped
upside down, with no initial spin, and still landed on its feet
Careful analysis of the photos reveals the secret. As the cat
rotates the front of its body clockwise, the rear and tail twist
counterclockwise, so that the total spin remains zero, in perfect
accord with Newton's laws. Halfway down, the cat
pulls in its legs before reversing its twist and then extends
them again, with the desired end result. The explanation was
that while no body can acquire spin without torque, a flexible
one can readily change its orientation, or phase. Cats know
this instinctively, but scientists could not be sure how it
happened until they increased the speed of their perceptions a
thousandfold.
31.What does the passage mainly discuss?
(A) The explanation of an interesting phenomenon
(B) Miracles in modern science
(C) Procedures in scientific investigation
(D) The differences between biology and physics.
32.The word "process" in line 10 refers to
(A) the righting of a tumbling cat
(B) the cat's fall slowed down
(C) high-speed photography
(D) a scientific experiment
33.Why are the photographs mentioned in line 16 referred to as an "experiment"?
(A) The photographs were not very clear.
(B) The purpose of the photographs was to explain the process.
(C) The photographer used inferior equipment
(D) The photographer thought the cat might be injured.
34.Which of the following can be inferred about high-speed photography in the late 1800's?
(A) It was a relatively new technology.
(B) The necessary equipment was easy to obtain.
(C) The resulting photographs are difficult to interpret.
(D) It was not fast enough to provide new information.
35.The word "rotates" in line 19 is closest in meaning to
(A) drops
(B) turns
(C) controls
(D) touches
36.According to the passage, a cat is able to right itself in midair because it is
(A) frightened
(B) small
(C) intelligent
(D) flexible
37.The word "readily" in line 24 is closest in meaning to
(A) only
(B) easily
(C) slowly
(D) certainly
38.How did scientists increase "the speed of their perceptions a thousandfold" (lines 25-26)?
(A) By analyzing photographs
(B) By observing a white cat in a dark room
(C) By dropping a cat from a greater height.
(D) By studying Newton's laws of motion.

Question 39-50
The changing profile of a city in the United States is apparent
in the shifting definitions used by the United States Bureau
of the Census. In 1870 the census officially distinguishe本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。