2．Some caterpillars' warning signals（信號）may have evolved（進化）from walking.
A team，writing in the journal Nature Communications，reported that the hair-like structures the living things use to make sounds evolved from legs.
The team studied caterpillars which use these structures to communicate their ownership of leaves.This means the caterpillars are able to"tell"strangers to go away without risking injury in fighting."These are really interesting caterpillars，"said Dr.Jayne Yack from Carleton University in Ottawa，Canada，who led the research."They make signals using hair-like structures which are on their back ends."
The caterpillars drag these structures across the leaf to make scraping（刺耳的）sounds when strangers enter the area of their leaves."When they make this signal，the strangers leave，"explained Dr.Yack."It's like saying'I'm here，get out of here-I already own this leaf '."
The scientists looked at other species（物種）within the same group of caterpillars and created their"family tree".They used chemical markers（標記物）to work out the relationship between the animals，showing which in the group were the more ancient species and which species evolved more recently."Those more ancient species actually don't have these sound-producing structures.
They have legs that they use to walk towards strangers，"said Dr.Yack.These more ancient species，she explained，walk towards strangers and try to fight against them."They can kill each other in the fighting，"Dr.Yack added.She said that the evolution of the scraping show had allowed the caterpillars to solve their fighting without injury."So our idea is that these signals actually avoid harm to both sides-they solve fighting in a more' friendly' way."
The study also provides a map of an evolutionary process that many other biologists are researching.
（1）What can we learn about caterpillars' warning structures from the text？
A．They have the same use as hair.
B．They are found in caterpillars' heads.
C．They are used to fight against strangers.
D．They may have evolved from caterpillars' legs.
（2）According to the text，Dr.Yack's team did NOT
.
A．draw a family tree of caterpillars
B．create a map to show how caterpillars evolve
C．study species within the same group of caterpillars
D．make clear the relationship between different species of caterpillars
（3）What does the underlined word"They"in the fifth paragraph refer to？
A．The ancient species.
B．The chemical markers.
C．The sound-producing structures.
D．The more recently evolved species.
（4）What is the main idea of the text？
A．How caterpillars evolved.
B．How caterpillars warn strangers.
C．Communication between caterpillars.
D．Caterpillars' warning signals evolved from walking.
