3．Scientists in the Netherlands have trained bees to identify COVID-19 through their sense of smell，according to a press release from Wageningen University.The research was conducted on more than 150 bees in Wageningen University's bio-veterinary research laboratory.
The scientists trained the bees by giving them a treat- a sugar-water solution- every time they were exposed to the scent of a mink （貂） infected with COVID-19.Each time the bees were exposed to a non-infected sample，they wouldn't get a reward.Eventually，the bees could identify an infected sample within a few seconds- and would then stick out their tongues like clockwork to collect the sugar water.
Bees aren't the first animals to detect COVID-19 by scent.Researchers have also trained dogs to distinguish between positive and negative COVID-19 samples from human saliva （唾液） or sweat with fairly high levels of accuracy.A small German study found that dogs could identify positive COVID-19 samples 94% of the time.That's because metabolic changes from the coronavirus make an infected person's bodily fluids smell slightly different from those of a non-infected person.But researchers still aren't sure whether animals are the best bet for sniffing out COVID-19 cases outside the lab.
"No one is saying they can replace a PCR machine，but they could be very promising，" Holger Volk，a neurologist，told Nature.；PCR machines are what lab technicians use to process standard COVID-19 swab tests.At the very least，certain animals could be useful for identifying COVID-19 in places or countries in which high-tech laboratory equipment is scarce or inaccessible.
Wageningen scientists are working on a prototype of a machine that could automatically train multiple bees at once.Then bees can use their skills to test for coronavirus aerosols （氣溶膠） in the surrounding environment.
（1）How did the researchers teach the bees to identify COVID-19？
A．By offering bees some rewards.
B．By infecting bees with COVID-19.
C．By raising bees with sugar water.
D．By exposing bees to infected humans.
（2）Why are dogs capable of finding out negative COVID-19 samples？
A．For dogs can sniff out hidden virus of the samples.
B．For dogs can tell the different smell of the samples.
C．For dogs can feel metabolic changes of the samples.
D．For dogs can distinguish saliva from sweat of the samples.
（3）What is the follow-up task of Wageningen scientists？
A．To breed more multiple bees.
B．To detect coronavirus aerosols.
C．To help underdeveloped countries.
D．To develop a new type of machine.
（4）Which can be a suitable title for the text？
A．A New Way to Cure COVID-19 Disease
B．Bees：Well-trained COVID- 19 Detector's
C．Bees' Extremely Accurate Sense of Smell
D．The Best Method of Identifying COVID-19
