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

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.

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.

______, 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

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

Which of the following is the best title for the passage?

A．How to Synthesize Fragrances

B．Synthetic Substances Are Easy to Make

C．Natural Flavorings and Fragrances

D．Synthetic Flavors and Fragrances

Which of the following is NOT true according to the last paragraph?

A．Synthetic fragrances can be used to make a used car smell like a new one.

B．Synthetic flavors and fragrances have added to the varieties of products.

C．Lemon soap is made out of some delicious lemon.

D．It is likely that a bottle of orange juice is synthesized.

Craig assured his boss that he would call______all his energies in doing this new job. forth at on off

As a defense against air-pollution damage, many plants and animals ______ a substance to absorb harmful chemicals. relieve release dismiss discard

Without the friction between their feet and the ground, people would in no ______be able to walk. time means way account

One reason for the successes of Asian immigrants in the U. S. is that they have taken great______to educate their children. means pains attempts hardships

The English language contains a(n)______of words which are comparatively seldom used in ordinary conversation. altitude latitude multitude attitude

The trouble is that not many students really know how to make use of their time to its best______ benefit advantage value profit

Though the imitation jewelry can fool many people, they cannot______up to an expert’s close examination. keep put stand pay

Your improper words will give______to doubts concerning your true intentions. rise reason suspicion impulse

Since Jonas Salk came up with his polio vaccine, infantile paralysis has virtually disappeared from the United States. surfaced with raised the price of discovered elevated

For all their protestations, they heeded the judge’s ruling. In spite of On behalf of Because of Without

The space shuttle program entails the use of sophisticated technology. enhances develops creates involves

When the Erie Canal was built in the 1820’s, it was the engineering marvel of its time. wonder dispute frustration model

As the proverb says: He that shuts love out, as a result, shall be shut out from love. in order in return in rotation in turn

The flowers in the vase shriveled because they hadn’t been watered for a week. decreased sweetened died shrank

The hard, out surface of the tooth is called enamel. outside appearance outer hiding

The earliest form of artificial lighting was fire, which also provided warm and protection. hot sunshine warmth safe

All mammals have hair, but not always evident. but it is not but it is but they are not but they are

The first recorded use of natural gas to light street lamps it was in the town of Frederick, New York, in 1825. was is it is were

He meant telling us about it, but he forgot to tell us. to be telling telling to have told having told

The rocket engine, with its steady roar like that of a waterfall or a thunderstorm, is an impressive symbol of the new space age. Rocket engines have proved powerful【C1】______to shoot astronauts【C2】______the earth’s gravitational【C3】______and put them on the moon. We have now【C4】______space travelers. Impressive and complex 【C5】______it may appear, the rocket, which was【C6】______in China over 800 years【C7】______, is a relatively simple device. Fuel that is【C8】______in the rocket engine changes【C9】______gas. The hot and rapidly expanding 【C10】______must escape, but it can do so only 【C11】______an opening that heads 【C12】______. As the gas is【C13】______with great force, it【C14】______the rocket in the【C15】______direction. Like the【C16】______of a gun when it is fired, it【C17】______the【C18】______ of nature described by Sir Isaac Newton when he found that “【C19】______every action, there is another equal and opposite【C20】______. “