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Natural flavorings and fragrances are often costly and limited in supply. For example, the vital ingredient in a rose fragrance is extracted from natural rose oil at a cost of thousands of dollars a pound; an identical synthetic substance can be made for 1% of this cost. Since the early twentieth century, success in reproducing these substances has created a new industry that today produces hundreds of artificial flavors and fragrances.
Some natural fragrances are easily synthesized; these include vanillin, the aromatic ingredient in vanilla, and benzaldehyde, the aromatic ingredient in wild cherries. Other fragrances, however, have dozens, even hundreds of components. Only recently has it been possible to separate and identit3, these ingredients by the use of gas chromatography and spectroscopy. Once the chemical identity is known, it is often possible to synthesize them. Nevertheless, some complex substances, such as the aroma of fresh coffee, have still not been duplicated satisfactorily.
Many of the chemical compounds making up these synthetics are identical to those found in nature, and are as harmless or harmful as the natural substances. New products must be tested for safety, and when used in food, must be approved by the U.S. Food and Drug Administration.
The availability of synthetic flavors and fragrances has made possible a large variety of products, from inexpensive beverages to perfumed soap to used cars with applied "new car odor."
71. From the passage we can learn that ______
A. natural flavorings and fragrances are not quite dear
B. the limitation of natural flavorings and fragrances is clear
C. the supply of natural flavorings and fragrances is adequate to meet the demand
D. the cost of producing natural flavorings and fragrances is high
72. Which of the following is true according to the passage?
A. Natural rose fragrance is 100 times more expensive to produce than artificial rose fragrance.
B. The most important ingredient in a rose fragrance is obtained from natural rose oil at a low cost.
C. A different synthetic substance can be made for 1% of the cost.
D. Natural rose oil costs the same as its fragrances.
73. The industry of producing hundreds of artificial flavors and fragrances probably appeared in ______
A. 2000 B. 1953
C. 1909 D. 1810
74. According to the passage, all the following are easier to synthesize EXCEPT ______
A. aromatic ingredient in vanilla
B. vanilla
C. aromatic ingredient in wild cherry
D. the flavor of fresh coffee
75. The underlined word "duplicated" in Paragraph 2 is closest in meaning to ______
A. make double
B. make a copy of
C. produce something equal to
D. take from
76. Why does the author mention fresh coffee in Paragraph 2?
A. As an example of complex substances having not been duplicated satisfactorily.
B. Because the coffee fragrance is hard to produce.
C. To conclude the passage.
D. The smell of fresh coffee is inviting.
77. ______ a substance can be synthesized.
A. Upon identifying the basic components of it
B. Once chemically analyzed
C. When gas chromatography is used
D. If spectroscopy is adopted
78. It can be inferred from the passage that ______
A. vanillin is easier to synthesize than benzaldehyde
B. not all synthetic flavors are harmless
C. in general, the less components there are in a fragrance, the harder it is to synthesize
D. synthesized substances must be tested for safety only if they are used in food
79. Which of the following is the best title for tile passage?
A. How to Synthesize Fragrances
B. Synthetic Substances Are Easy to Make
C. Natural Flavorings and Fragrances
D. Synthetic Flavors and Fragrances
80. Which of the following is NOT true according to the last paragraph?
A. Synthetic fragrances can be used to make a used car smell like a new one.
B. Synthetic flavors and fragrances have added to the varieties of products.
C. Lemon soap is made out of some delicious lemon.
D. It is likely that a bottle of orange juice is synthesized.
Some people associate migration mainly with birds. Birds do travel vast distances, but mammals also migrate. An example is the caribou, reindeer that graze on the grassy slopes of northern Canada. When the weather turns cold, they travel south until spring. Their tracks are so well-worn that they are clearly visible from the air. Another migrating mammal is the Alaska fur seal. These seals breed only in the Pribilot Islands in the Bering Sea. The young are born in June and by September are strong enough to go with their mothers on a journey of over 3,000 miles. Together they swim down the Pacific Coast of North America. The females and young travel as far as southern California. The males do not journey so far. They swim only to the Gulf of Alaska. In the spring, males and females all return to the islands, and there the cycle begins again. Whales are among the greatest migrators of all. The humpback and blue whales migrate thousands of miles each year from the polar seas to the tropics. Whales eat huge quantities of plankton. These are most abundant in cold polar waters. In winter, the whales move to warm waters to breed and give birth to their young.
81. From the passage we can learn that ______
A. people migrate like animals
B. only birds migrate
C. the female fur seals migrate only to the Gulf of Alaska
D. not all mammals migrate
82. The phrase "An example" underlined in Paragraph 1 refers to an example of a ______
A. migratory mammal
B. place where animals migrate
C. migrating bird
D. person who associates migration with birds
83. All the mammals are mentioned as migrating ones EXCEPT ______
A. caribou B. fin whale
C. reindeer D. Alaska fur seal
84. Where can you see from the air the migration of the mammals?
A. In the Pribilot Islands. B. In the Bering Sea.
C. In southern California. D. In northern Canada.
85. Which of the following is NOT true?
A. Whales breed in winter.
B. Young whales are given birth in cold waters.
C. Alaska fur seals give birth to the young only in one area.
D. Alaska fur seals are born in warm weather.
86. Together ______ of Alaska fur seals swim down the Pacific Coast of North America.
A. mothers and the young
B. fathers and the young
C. parents and the young
D. seals and whales
87. Which of the following is NOT described in the passage?
A. Whales migrate to breed and give birth to their young.
B. Whale-watching in Boston in summer is attracting.
C. Seals breed in the north before migration.
D. Reindeer feed on grass.
88. Whales live on ______
A. tiny plants and animals in the sea
B. the grassy slopes of northern Canada
C. their young in cold winter
D. the abundant seafood in tropic waters
89. How many kinds of migrating mammals are mentioned in the passage?
A. Four. B. Three.
C. Two. D. One.
90. What is the best title of the passage?
A. Three Types of Whales
B. Birds Migration
C. Mammals Also Migrate
D. Several Kinds of Migration
n. 毛皮，软毛，皮衣，毛皮制品
vt. 用毛
