托福听力资料.doc

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托福听力资料


★***英语听力频道为大家整理的托福听力资料。更多阅读请查看本站英语听力频道。
This morning I want to tell you about a r 第1页 /总页数 2 页
托福听力资料


★***英语听力频道为大家整理的托福听力资料。更多阅读请查看本站英语听力频道。
This morning I want to tell you about a recent scientific discovery dealing with the relationship between plants and animals. This is about a desert shrub whose leaves can shoot a stream of poisonous resin a distance of six feet. You think it would be safe from all attacks by insects? But a recent study has found one insect, a beetle that can chew its way past the plant's defense system by cutting the main vein that delivers the poison to the leaves. This vein cutting is just one method the beetles used to prepare a safe meal. Another is by cutting a path all the way across the leaves to hold the flow of chemicals. Then they simply eat between the veins of poison. In the past, scientists who studied insect adaptation to plant defenses have focused on chemical responses. That is, how the insects can neutralize or alter the poisonous substances plants produce. What's unique about this chewing strategy is that the beetle is actually exhibiting a behavioral response to the p