Passage Two
A beetle invasion in the United States has killed at least twenty million ash trees. The invasion of the emerald ash borer was first discovered near Detroit, Michigan, in 2002. Experts believe the small green insects arrived in the 1990's in shipments of goods from China.
The emerald ash borer has destroyed trees in the Midwest and as Far East in the United States as Maryland. [29]The insects have also spread as far north as Ontario, Canada.
Ash trees can resist many diseases. But they cannot resist the emerald ash borer. It lays eggs on the bark. The young larva drill into and feed on the inner bark. This harms the ability of the tree to transport water and nutrition.
In some places, farmers are using "detection trees". They have an area where bark has been cut away. The area circles the tree. [30]The process weakens the tree. It makes them easier targets for borers, and shows if the insects are nearby.
Efforts to stop the spread of the emerald ash borer include cutting down affected trees. There are worries that the ash tree might disappear unless the invasion is controlled. To prepare for such a possibility, a government laboratory is asking people to send in the seeds from ash trees. [31]It examines and x-rays the seeds to make sure there are no living borer fertilized eggs. Only the best seeds are remained and then sent for storage in a seed bank. There, they are dried and frozen. Should the seeds ever be needed, the hope is that scientists might someday develop an ash tree that could resist the little green attackers.

Questions 29 to 31 are based on the passage you have just heard.
29. How far do the insects spread northward?
正確答案：D
解析：短文說，鉆孔蟲向北擴散至Ontario，Canada。故D是正確答案。四個選項是地名，可猜測題目與地點有關。A和C是美國的州名，B和D是國家名，邊聽邊做好筆記。解題的關鍵在于聽清楚問題，就可以對號入座找出正確的答案了。
30. Why is part of the bark cut away?
正確答案：C
解析：短文說，鉆孔蟲是在樹上產卵子，孵出的幼蟲鉆到內層樹皮吸取營養，故把部分樹皮削去會使樹更容易成為攻擊的目標，當鉆孔蟲來襲時就能有所發覺。故C是正確答案。從選項可以初步猜測題目與樹木和昆蟲有關。解題時需聽清楚問題問的是什么。
31. What is the government laboratory trying to do?
正確答案：B
解析：短文說，實驗室對種子進行檢查和照x-ray，確保沒有鉆孔蟲的受精卵，只有最好的才被保存起來。故答案是B。從選項可以初步猜測題目與措施有關。“Only”表明文章要提出特殊的要點了，要提高警惕。