48 What does the word "permafrost" in the second paragraph most likely mean?
(A) A hard shiny metal that exists in the ground.
(B) A layer of soil and rock that stays icy forever.
(C) A place where water from a river falls down over a cliff.
(D) A straight surface that has one side higher than the other.

China completed完善、完整 the construction建築物、構造，結構 of the Qinghai-tibet西藏 Railroad in 2006. This 1,142-km railroad line runs across the snow-covered plateau平地, 高原、平穩、停滯期 of Tibet, effectively linking the Tibetan capital, Lhasa, to the northwestern province of Qinghai. Also known as the Pan-Himalayan Railroad, this record-breaking railroad rises to 5,072 meters, earning the title as the world's highest passenger train with more than eighty percent of the track 13,000 feet or 3,962 meters above sea level.

The Qinghai-Tibet Railroad is a great engineering achievement成就，成績. Since it was built at high altitudes海拔 both engineers and workers had to breathe bottled oxygen for fear of altitude sickness while working on the construction建築物、構造，結構 of the track道路、小徑、跑道、足跡、方向. Additionally另外, there were many other challenges they had to cope with, including the soil that can rise and sink沈沒, 、陷入 as the season changes. Some sections部分；片段 of track had to be laid on ground that is permanently frozen.

Due to global warming, the rising temperatures may cause this permafrost永凍層，永凍土層 to melt, making the land sink to a lower level. The track may become bent彎曲 or curved as a consequence（常指不好或不利的）結果. Nevertheless不過，仍然、儘管, some smart countermeasures對策 were taken so that the engineers managed to cool off the roadbed路基 by keeping the permafrost stable. The cost savings to travelers resulting from來源于 the completion完成；結束 and operation of the Qinghai-Tibet Railroad are tremendous巨大的；極好. Compared with typical fares for direct air travel, a typical train fare between Beijing and Lhasa is much cheaper. Moreover, travelers get to enjoy the magnificent極好的；壯麗 sights and scener風景、劇院 along the way, making the long trip more than worthwhile值得. It is hoped that with better linkage聯繫 to the world, the tourism industry will play an increasingly important role in Tibet's economy.

48 第二段中的“永久凍土”一詞最有可能是什麼意思？ 

(A) A hard shiny metal that exists in the ground. (B) A layer of soil and rock that stays icy forever. (C) A place where water from a river falls down over a cliff. (D) A straight surface that has one side higher than the other.

(A) 存在於地下的堅硬閃亮的金屬。

(B) 一層永遠保持冰冷的土壤和岩石。

(C) 河水從懸崖上傾瀉而下的地方。

(D) 一側比另一側高的直表面。