单选题
Where Have All the Bees Gone?

Scientists who study insects have a real mystery on their hands. All across the country, honeybees are leaving their hives and never returning. Researchers call this phenomenon Colony Collapse Disorder. According to surveys of beekeepers across the country, 25 to 40 percent of the honeybees in the United States have vanished from their hives since last fall. So far, no one can explain why.
Colony collapse is a serious concern because bees play an important role in the production of about one-third of the foods we eat. As they feed, honeybees spread pollen from flower to flower. Without this process, a plant can't produce seeds or fruits.
Now, a group of scientists and beekeepers have teamed up to try to figure out what's causing the alarming collapse of so many colonies. By sharing their expertise in honeybee behavior, health, and nutrition, team members hope to find out what's contributing to the decline and to prevent bee disappearance in the future.
It could be that disease is causing the disappearance of the bees. To explore that possibility, Jay Evans, a researcher at the United States Department of Agriculture (USDA) Bee Research Laboratory, examines bees taken from colonies that are collapsing. "We know what a healthy bee should look like on the inside, and we can look for physical signs of disease," he says. And bees from collapsing colonies don't look very healthy. "Their stomachs are worn down, compared to the stomachs of healthy bees," Evans says. It may be that a parasite is damaging the bees digestive organs. Their immune systems may not be working as they should. Moreover, they have high levels of bacteria inside their bodies.
Another cause of Colony Collapse Disorder may be certain chemicals that farmers apply to kill unwanted insects on crops, says Jerry Hayes, chief bee inspector for the Florida Department of Agriculture. Some studies, he says, suggest that a certain type of insecticide affects the honeybee's nervous system (which includes the brain) and memory. "It seems like honeybees are going out and getting confused about where to go and what to do," he says.
If it turns out that a disease is contributing to colony collapse, bees, genes could explain why some colonies have collapsed and others have not. In any group of bees there are many different kinds of genes. The more different genes a group has, the higher the group's genetic diversity. So far scientists haven't determined the role of genetic diversity in colony collapse, but it's a promising theory, says Evans.

单选题 What is the mystery that researchers find hard to explain?

A.Honeybees are flying all across the country.
B.25%—40% of the honeybees in the U.S. have died.
C.Honeybees are leaving their hives and do not return.
D.Honeybee hives are in disorder.

单选题 Why are researchers seriously concerned with the phenomenon of Colony Collapse Disorder?

A.Because honeybees produce one-third of the foods we eat.
B.Because honeybees feed on flowers.
C.Because honeybees eat seeds of flowers.
D.Both B and C.

单选题 What are the possible causes of Colony Collapse Disorder given by the scientists?

A.Worsening environment.
B.Disease and chemicals.
C.Dwindling number of flowers around.
D.Changes in genes' structures.

单选题 According to the fifth paragraph, which of the following about bees' genes is TRUE?

A.Bees' genes allow them to expand their colonies.
B.Bees' genes help keep them in their hives.
C.Bees' genes make them fly from flower to flower.
D.Bees' genes could explain the collapse of some colonies.

单选题 What explanation is given by Jerry Hayes to the phenomenon?

A.Farmers apply certain chemicals to kill unwanted bees.
B.The insecticide destroys the honeybee's nervous system.
C.The insecticide affects the honeybee's memory.
D.All of the above.