The Sailing Stones of Death Valley 美國死亡谷「會走路的石頭」 For decades, scientists wondered how these stones moved on their own. 數十年來，科學家們都好奇這些石頭到底是如何自行移動的。
There is a place in the United States called the Racetrack Playa in the northwest corner of Death Valley National Park. It's a dried-up lake in one of America's hottest, driest, and lowest places. It's also home to rocks that move across the ground all by themselves.
These strange rocks have been known for years to move across the dry ground and leave behind long, twisting▼ trails. There have been many explanations▼ for their strange movement, including everything from heavy winds to strange ice formations▼. Some people even thought it might be aliens▼ or some magical force. In 2014, two scientists set up an experiment▼ to figure it outonce and for all.
What the scientists found was that, under very particular weather conditions▼, rain would freeze overnight into thin sheets of ice. Then in the morning, the sun would warm the ice, which enables even a breeze to move the rocks across the partly▼ melted ice. The results finally explained the mystery▼ of Death Valley's sailing rocks as well as similar moving rocks around the world. While aliens moving rocks across the desert would have been amazing, the complex science behind the sailing stones is also pretty cool.
▼ twisting a. 蜿蜒曲折的 ▼ explanation n. 解釋；理由 ▼ formation n. 形成物 ▼ alien [ `elIJn ] n. 外星人 ▼ experiment n. 實驗 ▼ condition n. 情況；條件 ▼ partly adv. 部分地 ▼ mystery n. 謎，神祕的事物
decade n. 十年
The toy company has been in business for two decades.
magical a. 神祕的；神奇的；有魔力的
No medicine is so magical that it can cure all illnesses.
figure...out / figure out... 查清楚／弄明白……
I can't figure out why Johnson won't move out of this dangerous neighborhood.
once and for all 徹底地，一勞永逸地
For your health, you should quit smoking once and for all.
particular a. 特殊的；特定的
This particular type of corn was introduced to the country 200 years ago.
freeze vi. & vt. 結冰，使結冰
When the temperature is below zero, water will freeze.
enable vt. 使能夠；使可能
The magical ring enabled the superhero to fly.
complex a. 複雜的；難以理解的
Professor Lai has the ability to express the most complex ideas clearly.
量詞 sheet 的用法
本文 "What the scientists found was that, under very particular weather conditions, rain would freeze overnight into thin sheets of ice." 中的 sheet 為冰的量詞，表「一層，一大片」的意思。除此之外，sheet 還可作為其他物品的量詞，表「一張，一片」。例：
a sheet of paper 一張紙
a sheet of glass 一片玻璃
a sheet of plastic 一片塑膠
A thick sheet of ice had formed over the water.
I need a blank sheet of paper to write answers on.