1 . When an ant dies, other ants move the dead insect out. Sometimes, the dead ant get moved away very soon—within an hour of dying. This behavior is interesting to scientists, who wonder how ants know for sure—and so soon—that another ant is dead.
One scientist recently came up with a way to explain this ant behavior. Dong-Hwan Choe is a biologist. Choe found that Argentine ants have a chemical on the outside of their bodies that signals to other ants, “I’m dead—take me away.”
But there’s a twist to Choe’s discovery. Choe says that the living ants—not just the dead ones —have this death chemical. In other words, while an ant crawls around, perhaps in a picnic or home, it’s telling other ants that it’s dead.
What keeps ants from dragging away the living ants? Choe found that Argentine ants have two additional chemicals on their bodies, and these tell nearby ants something like, “Wait—I’m not dead yet.” So Choe’s research turned up two sets of chemical             signals in ants: one says, “I’m dead,” and the other set says, “I’m not dead yet.”
Other scientists have tried to figure out how ants know when another ant is dead. If an ant is knocked unconscious, for example, other ants leave it alone until it wakes up. That means ants know that unmoving ants can still be alive.
Choe suspects that when an Argentine ant dies, the chemical that says “Wait- I’m not dead yet” quickly goes away. Once that chemical is gone, only the one that says “I’m dead” is left. “It’s because the dead ant no longer smells like a living ant             that it gets carried to the graveyard, not because its body releases new unique chemicals after death,” said Choe. When other ants detect the “dead” chemical without the “not dead yet” chemical, they drag away the body.
Understanding this behavior may help scientists figure out how to stop Argentine ants from invading new places and causing problems. Choe would like to find a way to use the newly discovered chemicals to spread ant killer to Argentine ant nests.
The ants’ removal behavior is important to the overall health of the nest. “Being able to quickly remove dead individuals and other possible sources of disease is extremely important to all animals living in societies, including us,” says Choe. “Think             about all the effort and money that we invest daily in waste management.”
1. The underlined word “twist” in Paragraph 3 means _____.

A．an unexpected change	B．a clear mistake
C．an important key	D．a shocking conclusion

2. Ants judge whether another one is dead or not depending on ______.

A．the sense of taste	B．the sense of smell
C．the sense of touch	D．the sense of sight

3. The result of the research can be used to ______.

A．kill troublesome pests

B．solve the problem of endangered species

C．prevent further expansion of the ants’ territory

D．keep the balance of nature

4. Why is it important to remove dead individuals?

A．Because it is easier to manage the living.

B．Because it can save money to deal with the waste.

C．Because it can provide more space for the living.

D．Because it can keep the living from suffering disease.

5. What might be the best title of the text?

A．Dead or living? It is easy to judge

B．Pulling away the dead ants is a difficult task

C．Ant nests have great undertaking capacity

D．Leaving it alone or taking it away? Ants feel puzzled