3、When a caterpillar （毛毛虫） feeds on a tomato leaf, the plant moves rapidly to meet with a defensive response, systematically releasing “proteinase inhibitors” – proteins that interfere （干扰） with the caterpillar’s digestion – throughout the plant, especially in the leaves. But how does the message get from the wounded leaf to the rest of the plant?

Most scientists believed the alarm was spread by chemical messengers until a team of researchers headed by David Weldon – a biologist at the University of East Anglia in Norwich, England – made a shocking discovery. An injured leaf, the researchers found, sends an electrical signal to warn neighboring leaves of upcoming danger. It’s a “terribly tiny current” driven by an electrical potential difference of only 20 millvots（瓦特）, says Weldon, who measured the voltage after electrodes were attached to the plan’s surface.

“Right now, all we can say is that there is a correlation,” Weldon notes. “If you wound the plant, you’ll see an electrical signal accompanied by a biochemical response.” To learn more about the reaction, Weldon’s team plans to insert electrodes within the plant tissue （rather than on the surface） to determine what’s going on at the cellular level. The findings may help explain other mysteries surrounding plants. For example, many plants start to flower in springtime, as days grow longer, but plants sense the change in the day length through their leaves, while flowers begin to bloom at the buds （蓓蕾）. “There must be a signal from the leaf to the growing points”, Weldon says. “So far, no one has come up with a convincing chemical mechanism. Maybe an electrical signal is involved.”

1．What is the function of the “proteinase inhibitors” in tomato plants?

       A．They create nutritional matter.

       B．They produce electrical signals.

       C．They protect the plant from insects.

       D．They cure diseases by changing chemicals.

2．The researchers discovered that          .

       A．the alarm was increased by chemical messengers

       B．the wounded leaf raised danger signals by tiny currents

       C．the whole plant was aware of the risk through different signals

       D．proteinase inhibitors expanded the warning to the plant’s surface

3．What question do scientists hope to answer with further research?

       A．Do plants send chemical messengers that register pain?

       B．Do plants create cell tissues that help rebuild the leaves?

       C．Do plants create proteinase inhibitors that warn them of danger?

       D．Do plants send electrical signals that tell them it is time to grow?

4．The best title of this passage is              .

       A．Electrical Tomatoes

       B．Endless Cycles of Plants

       C．A debatable Research

       D．A Magic Role of Caterpillars