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【单选题】
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.' 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
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【单选题】以下关于卵巢的说法正确的是
A.
卵巢只产生卵子,不分泌激素
B.
卵巢表面由腹膜覆盖
C.
青春期前卵巢表面光滑
D.
髓质在中心,内有数易万计的始基卵泡
E.
皮质在外面,内有丰富的血管
【单选题】关于卵巢的说法正确的是()
A.
是腹膜外位器官
B.
卵巢动脉起于髂内动脉
C.
借卵巢固有韧带连于子宫底的两侧
D.
后缘有血管出入
【单选题】2013年1月1日,甲公司对乙公司的长期股权投资改为权益法核算后,该长期股权投资的账面价值为( )万元。
A.
29200
B.
19260
C.
20700
D.
21360
【单选题】V-M无静差调速系统中,PI调节器中的电容元件发生短路后,对系统影响是
A.
仍为无静差系统
B.
变为有静差系统
C.
无法调速
D.
电动机过流
【判断题】人类这么脆弱的生物,之所以能够比狮子、老虎更厉害,是因为他们懂得外包大脑。这种说法是否正确?
A.
正确
B.
错误
【判断题】When the author met Joe Delaney and Harry Belafonte, they were already very successful.
A.
正确
B.
错误
【单选题】V-M无静差调速系统中,PI调节器中的电阻元件发生短路后,对系统影响是
A.
仍为无静差系统
B.
变为有静差系统
C.
无法调速
D.
电动机过流
【单选题】关于卵巢排卵时间的说法正确的是
A.
月经前14天
B.
随时可能,不固定
C.
月经干净后
D.
月经期前
【单选题】关于卵巢的说法正确的是()
A.
排卵一定是由两侧卵巢轮流进行
B.
排卵发生在月经过后14天
C.
黄体约在排卵后9~10天达高峰
D.
卵泡成熟,宫颈黏液量由多变少
E.
黄体能产生孕激素和雌激素
【多选题】关于卵巢的说法正确的是
A.
是女性的生殖腺
B.
位于卵巢窝内
C.
呈扁的卵圆形
D.
能产生卵子
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