Special trees that grow faster, fight pollution, produce better wood, and even sense chemical attacks are being planted by scientists in the US．
When 40 per cent of Hawaii's US$14 million-a-year papaya （木瓜）industry was destroyed by a virus five years ago, work began on creating genetically engineered（转基因的）trees．
Researchers successfully introduced seeds that were designed to resist the virus．Since then, more and more people have been testing genetically engineered trees．Some researchers put special bacteria into trees to help them grow faster and produce better wood．Others are trying to create trees that can clean polluted soil．Meanwhile fruit farmers are looking for trees that are strong enough to resist worms, and paper companies want trees that produce more wood and therefore more paper．
The Pentagon （五角大楼） even gave the researchers US$500,000 this year after they developed a pine tree that changes its colours if it senses a chemical attack．So far, the poplar, eucalyptus （杨树与桉树）, apple and coffee trees are among those being engineered．All this can be done today because we have a better understanding of tree genomes （基因组）．
However, some people fear that the genetically engineered trees will cause dangerous results．They are worried that the new trees will breed with natural species and change the balance of the forest environment．
“It could be destructive,” said Jim Diamond, an environmentalist. “Trees are what is left of our natural environment and home to many endangered species.”
But researchers insist that science could give nature a fighting chance against both natural and man-made dangers．They hope to answer the critics by stopping the new trees from breeding, so their effect on the environment can be controlled．
63．Which kind of tree is not the ones that scientists are planting in the US?
A．Trees that worms can't hurt．
B．Genetically engineered trees．
C．Trees that can resist wind better．
D．Trees that can protect themselves at a chemical attack．
64．What caused the American scientists to work on special trees?
A．Tree genomes are mapped out so scientists know how to improve trees．
B．Great numbers of trees have been lost due to attacks by viruses．
C．Researchers successfully introduced seeds designed to resist the virus．
D．They think science could give nature a fighting chance against both natural and man-made dangers．
65．Which of the following was probably the first kind of trees being engineered?
A．Papaya． B．Pine． C．Apple． D．Poplar．
66．Why did critics think engineered trees dangerous? Because ________．
A．these trees can destroy the balance of nature
B．everything except trees has been genetically engineered
C．trees are home to many endangered species
D．these trees may affect normal trees
