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