Question

　　Destructive insects in larger numbers are finding Alaska forests to be a comfortable home and climate change could be the wel-come mat.

　　Warmer winters kill fewer insects. Lon-ger, warmer summers let insects complete a life cycle and reproduce in one year instead of two. Warm winters also can damage trees and make them less able to stop insect attacks by changing the nature of snow. Instead of light snow formed at extremely cold tempera-tures, warm winters produce wet, heavy snow more likely to break the tops of spruce trees because they are not well adapted to handling big, heavy, wet snow loads.

　　Since 1980, spruce bark (树皮) beetles have killed mature white spruce trees on 4. 4 million acres. For lack of two cold winters on end, the numbers of the beetles there blew up while the resistance (抵抗力) of the trees was down at the same time everywhere. Most of the mature trees have been killed in some whole region of the state.

　　Spruce bark beetles bore into (蛀穿)trunks and feed on the live cambium layer, a thin part of tissue between bark and wood. Trees re-sist beetles with pitch, made up of hydrocarbons including up to 17 forms of terpene (松稀). The rates of those terpenes are a signal of the health of the tree. When a tree is injured, terpene rates go off in one direction.

　　Using complex chemical receptors (感受 器), spruce bark beetles discover differences in terpenes. Injured trees offer less resistance.

　　They smell the tree. If the tree's healthy,they try to avoid it Why? If they start to bore into a healthy tree, it's got a lot of pitch, and the pitch is under high pressure. It's boring in and the pitch is pushing it back out.

(1) What would be the best title for the text?

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A．The Destruction of Forests in Alaska

B．Warm Winters and Its Bad Effects

C．The Way of Spruce Trees' Living in Alaska

D．Destructive Insects on Rise in Alaska

(2) According to the text, how do warm win-ters reduce the trees' ability to resist in-sect attacks?

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A．By changing the nature of snow.

B．By offering too much water to trees.

C．By making the weather drier.

D．By increasing the insects' growth speed.

(3) The third paragraph mainly tells________.

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A．winters are warmer and warmer

B．there are more and more beetles

C．the situation of trees is much worse

D．mature trees are easy to be attacked

Answer 1

答案：D;A;C
解析：

(1) 本题要求选择最佳标题。本文主要讲述了破坏性的昆虫渐渐地适应了阿拉斯加的气候， 数量在不断增加，而且部分昆虫对树木进行了大量的破坏，危及当地的森林。故D正确。 (2) 细节理解题。根据文章第二段中“stop in-sect attacks by changing the nature of snow”可知，warm winters通过改变降雪的性质降低了树木阻止昆虫侵袭的能力。故A正确。 (3) 段落大意题。由文章第三段可知自1980年以来，树木的形势越来越严峻，因为很多的树木已经死亡，故C正确。