$\left(\frac{1}{{\text{x}}^2\text{-}2\text{x}}\text{-}\frac{1}{{\text{x}}^2\text{-}4\text{x}+4}\right)$ ÷ $\frac{2}{{\text{x}}^2\text{-}2\text{x}}$ ,其中x=2(tan45°-cos30°).

This is part of a book's table of contents.

Chapter One: North America
The Fox and the Raccoon .....      1
Song of the Mountains .........      4
Little Feather Meets Bear .....       7
Chapter Two: South America
Kuma and the Big River.........     10
The Smallest Monkey ............    12
Three Tree Frogs ...................    15
Chapter Three: Africa
Marumbi Saves the Day.......        18
The Jumping Fish ................      22
Father Lion and His Son ......       25

空气中含量较多且化学性质不活泼的气体是

近代化也叫现代化，其主要表现为经济领域的工业化，政治领域的民主化和法制化，思想文化领域的理性化和科学化等，实现近（现）代化是近代以来世界各国发展的必由之路。