D．give off nice chemicals to attract friendly insects to attack the pest

　　【解析】　事实细节题。由第三段"when a plant senses that it's being eaten, it cannot walk away from trouble; on the contrary, it will release a chemical vapor"及倒数第二段"Those chemicals attract friendly insects that attack the pests eating the plant."一句可知，当植物被昆虫吞食的时候，植物会释放出一种化学蒸汽来吸引有益的昆虫袭击害虫。故选D。

　　【答案】　D

　　3. The underlined word "alerts" most probably means "______"．

　　A．warns　　　　　　　 B．protects

　　C．threatens D．allows

　　【解析】　词义猜测题。根据前后文意可知，植物在遭受攻击时会释放一种化学物质，这种物质有两种功能：警示危险的存在和发出求助信息。由此可知答案为A。

　　【答案】　A

　　4．Which would be the best title for the passage?

　　A．Communication between Plants

　　B．A Chemical "Language"

　　C．Plants Can Talk

　　D．How Plants Protect Themselves

　　【解析】　标题归纳题。短文讲述的主题是植物的特殊语言及功能。因此C项概括了文章主题同时又生动风趣，尤其是talk一词充满了拟人化的幽默感。故答案为C。

　　【答案】　C

　　B

If you talk about a dog's life，go to Beijing to see the pampered(过分娇惯的)dogs.Dogs clipped，dressed up，washed and dried.Here, it's the owners who go to the