一只家系不明的雄性白兔与若干只纯种雌性灰兔杂交，生出19只白兔和22只灰兔。根据此信息，你认为这能说明（）
A.雄性白兔是纯合子
B.白兔为隐性性状
C.灰色是隐性性状
D.什么也不能说明
参考答案：C
解析：若雄性白兔是纯合子，与纯种雌性灰兔杂交，则子代应该只出现白色或灰色一种体色，A错。若白兔为隐性性状，与纯种雌性灰兔杂交，则子代应该只出现灰色，B错。若灰色为显性性状，且为纯种，子代应该只有灰色．但题中说明两种颜色都有，所以灰色是隐性性状，所以选C．考点：本题主要考查了显隐性性状的判定，充分题目中的条件，学以致用。能运用所学知识与观点，通过比较、分析与综合等方法对某些生物学问题进行解释、推理，做出合理的判断或得出正确的结论
| 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