如图所示的微观化学变化，其基本反应类型属于（ ）
A．分解反应
B．置换反应
C．化合反应
D．复分解反应
答案：A
题目分析：化合反应是有两种或两种以上的物质生成一种物质的化学反应，特征是：多变一．分解反应是一变多；由微观模拟图可知，一种化合物分子生成了两种单质分子，属于分解反应．
故选A
点评：本考点考查了基本反应类型的判断，要牢记四个基本反应类型的概念，并会理解应用．本考点基础性比较强，主要出现在选择题和填空题中．
| 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." |
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.