问题
单项选择题
| 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 identify 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." |
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
答案
参考答案：B
解析：
[分析]： 推断题型。 见第三段第一句：Many of the chemical compounds…and are as harmless or harmful as the natural substances．由此推断出；有些化学合成物(其中也包括香料)与其自然界存在的物质一样是无害的，有些则是有害的。因此选项B为答案。