题目内容：

    Spring is here, the colourful flowers are seen everywhere but it is a pity that many of us are not able to smell them while enjoying the colourful flowers.

Growing levels of air pollution from the factories and cars have reduced flower fragrances(芳香) by up to 90 percent in the US, compared with pre-industrial levels 100 years ago.

But if the trend is simply unpleasant for human noses, it may be life-dangerous for bees and butterflies.

Many insects find flowers by following the scent produced by those flowers.

The increasing pollution makes it difficult for them to find the flowers and feed on their nectar (花蜜).

Scientists have already found that flowers produce scent molecules (气味分子) that mix with polluted things, which breaks down the plants’ sweet smell.

With more pollution in the air, the scent molecules don’t remain powerful as long and travel shorter distances on the wind. In the mid-19th century, when pollution levels were first recorded, scent molecules would have been able to travel some 1,000 to 1,200 meters. Today, in the polluted air of large cities, scents may only make it some 200 to 300 meters.

Also, pollution from polluted air may fool the bee’s “nose”, making their search for flowers all the more difficult.

In a paper published recently in Scientific Reports, scientists said that the nitric oxide (NO) and nitrogen dioxide (NO2) in polluted air could change many chemicals that work together to give a flower its special smell.

“This”, researchers said, “could prevent honeybees from reaching their flowers and prevent the pollination (授粉) of some of the world’s food crops.” Or, this could put in danger agricultural harvests worldwide.

But the bees seem to have learned to get used to the changing world. “In nature honeybees use their special eyes and flower smell to find out where a flower is for the first time,” the researchers said.

1.According to the article, researchers have recently found that ________.

A.reduced flower fragrances have resulted in the dying out of many bees and butterflies

B.reduced flower fragrances are connected to growing levels of air pollution

C.polluted things in the air prevent flowers from producing scent molecules

D.flowers today can’t produce enough nectar because of air pollution

2.What do the underlined words “the trend” in Paragraph 3 refer to (指的是)?

A.Increasing air pollution.

B.Reduce flower fragrances.

C.Human beings’ worse sense of smell.

D.A growing number of power plants and cars.

3.The scent molecules a plant produces are mainly to ________.

A.help flowers to produce nectar B.prevent insects from eating the plant

C.draw attention from bees and butterflies D.clear up polluted things in the air

4.We can infer (推断) from the article that ________.

A.future food crops won’t depend on bees to complete their pollination

B.bees have great advantages in their senses compared to humans

C.world food crop production is likely to fall greatly in the near future

D.some bees have successfully get over the challenge of reduced flowers fragrance