When you watch TV programs about wild animals, it is surprising to see how an antelope can escape a lion’s attack. In the wilderness, everyone has a stunt(绝招). Even plants have their own ways of fighting off enemies.
Over millions of years of evolution(进化), plants have developed a unique defence system. Chemicals are widely used for survival. By making their leaves, flowers, roots and fruits poisonous to enemies, plants can fight back.
One such plant is the Golden Wattle tree, British scientist David Caneron has found when an animal eats the tree’s leaves, the amount of poison increase in the other leaves. “It’s like the injured leaves telephoning the others telling them to fight together against the enemy,” he said.
The tree also sends defence messages to neighboring plants by giving out a special smell. Golden Wattle trees in the nearby 45 meters will get the message and produce more poison within 10 minutes. Now, if an enemy eats too many of the trees’ leaves, it will die.
Every species of plant or tree is good at producing a special set of chemicals. A herbivore that can safely eat the leaves of one tree may be poisoned by its neighbor.
In this way, plants have developed not only their own defence system, but also shared with others. This makes it impossible for a single animal to destroy even a small area of forest.
30. According to the study, if one Golden Wattle tree is attacked by animals, it can ________.
A. tell other trees to protect it
B. produce more poison within 10 minutes
C. sent defence messages to the neighboring plants
D. kill the animals with its leaves
31. In this passage the underlined word “herbivore” probably means animals which________.
A. live on both animals and plants.
B. feed on smaller animals
C. live on trees.
D. feed on plants or grass
32. The last paragraph of the passage suggests that this kind of defence system________.
A. does great harm to the animals
B. does good to the forests
C. is helpful to some animals
D. harms the forests