6. Travelling at a height of 30,000 feet, far above the clouds, and at over 500 miles an hour is an

exhilarating experience.

句中at a height of 30,ooo feet和at over 500 miles an hour为两个并列的介词短语作状语，修饰动名词主语

travelling，并与其一同构成动名词短语，在句子中作主语。

文中far above the clouds作插入语，对at a height of 30,000 feet作补充说明。

7. However you decide to spend your time, one thing is certain: you will arrive at your destination

fresh and uncrumpled.

However意为"不管，无论", 为连接动词，引导让步状语从句。

fresh and uncrumpled意为"精神焕发，毫无倦意"

冒号后面的部分为one thing的同位语。