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            C
 When an ant dies, other ants take it out of the nest, often within an hour after its death. This behavior interests scientists and they 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, a scientist who studies animals and plants. He found that ants have a chemical on the outside of their bodies that signals to other ants, “I'm dead—take me away” when it is dead.
But there's a question to answer: As we know, if an ant is dead, it stops moving. But when an ant is sleeping or knocked unconscious, it is also not moving. However, other ants don't move the living ant out of the nest. How do they know this ant is not dead? Choe found that ants have another chemical on their bodies, which tells nearby ants something like, “Wait—I'm not dead yet” when it is not dead. Choe suspects that when an ant dies, the chemical that says, “Wait I'm not dead yet” quickly goes away. When other ants detect the “dead” chemical without the “not dead yet” chemical, they move away the body.
To test his theory, Choe and his team put different chemicals on ants. When the scientists used the “I'm dead” chemical, other ants quickly moved the treated ant away. When the scientists used the “Wait—I'm not dead yet” chemical, other ants left the treated ant alone. Choe believes this behavior shows that the “not dead yet” chemical overrides the “dead” chemical when picked up by other ants. And that when an ant dies, the “not dead yet” chemical fades away. Other nearby ants then detect the remaining “dead” chemical and remove the body from the nest.
Understanding this behavior can help scientists figure out how to stop ants from invading new places and causing problems.
28．What is the function of the first paragraph?
A. Leading the following paragraphs.
B. Showing the main idea of the passage.
C. Introducing the background of the passage.
D. Giving a summary of the passage.
29．What can we learn from the passage?
A. Living ants can also be taken away when they are not moving.
B. When an ant dies, it can tell others using a certain chemical.
C. A living ant can pretend to be dead using a special chemical.
D. Ants often use chemicals to communicate with each other.
30．Which of the following descriptions about Dong-Hwan Choe is right?
A. Choe did this study in order to stop ants from invading new places.
B. Choe is a biologist who is only interested in animals, especially in ants.
C. Choe first came up with an idea to explain this ant behavior，and then did some tests to prove his theory.
D. Choe did the research on this ant behavior on his own
31．What is mainly discussed in the passage?
A. How to decide whether an ant is dead or not.
B. Why ants have special chemicals on their bodies.
C. reasons for the removable behavior of ants.
D. How ants manage to keep their nests clean.
                                D               
Women are friendly. But men are more competitive. Why? Researchers have found it's all down to the hormone oxytocin (荷尔蒙催生素). Although known as the love hormone, it affects the sexes differently.
"Women tend to be social in their behavior. They often share with others. But men lend to be competitive. They are trying to improve their social status," said Professor Ryan.
Generally, people believe that the hormone oxytocin is let out in our body in various social situations and our body creates a large amount of it during positive social interactions (互动) such as falling in love or giving birth.
But in a previous experiment Professor Ryan found that the hormone is also let out in our body during negative social interactions such as envy.
Further researches showed that in men the hormone oxytocin improves the ability to recognize competitive relationships, but in women it raises the ability to recognize friendship.
Professor Ryan's recent experiment used 62 men and women aged 20 to 37. Half of the participants（参与者）received oxytocin. The other half received placebo (安慰剂).
After a week, the two groups switched with participants. They went through the same procedure with the other material.
Following each treatment, they were shown some video pictures with different social interactions. Then they were asked to analyze the relationships by answering some questions. The questions were about telling friendship from competition. And their answers should be based on gestures, body language and facial expressions.
The results indicated that, after treatment with oxytocin, men's ability to correctly recognize competitive relationships improved, but in women it was the ability to correctly recognize friendship that got better.
Professor Ryan thus concluded: "Our experiment proves that the hormone oxytocin can raise people's abilities to better distinguish different social interactions. And the behavior differences between men and women are caused by biological factors (因素) that are mainly hormonal."
32. What causes men and women to behave differently according to the text?
A. Placebo.  B. Oxytocin.   C. The gesture.    D. The social status.
33. What can we learn from Professor Ryan's previous experiment?
A. Oxytocin affects our behavior in a different way.
B. Our body lets out oxytocin when we are deep in love.
C. Our body produces oxytocin when we feel unhappy about others' success.
D. Oxytocin improves our abilities to understand people's behavior differences.
34. Why did Professor Ryan conduct the recent experiment?
A. To test the effect of oxytocin on the ability to recognize social interactions.
B. To know the differences between friendship and competition.
C. To know people's different abilities to answer questions.
D. To test people's understanding of body language.
35. The author develops the text by______.
A. explaining people's behaviors  B. describing his own experiences
C. distinguishing sexual differences  D. discussing research experiments
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