Planting trees

pass down [= hand down]（流传）

　　This custom has been passed down since the 17th century.

　　13. indispensable（不可缺少的）

　　Air is indispensable to life.

　　

　　二、语法句型解析：

　　1. A is to B what C is to D. = A is to B as C is to D. = As C is to D,

　　so is A to B.  = What C is to D, A is to B.

　　（A之于B就如同C之于D）

　　Reading is to the mind as food is to the body.

　　2. It + be + 表强调的词语 + that ......

　　 It was not until yesterday that I knew he had gone to America.

　　3. enable + 宾语 + to-V（动词原形）（使能够）

　　The internet enables us to gain the latest information.

　　4.Were it not for ….. = If it were not for….. = But for….. = Without

　　…

　　[假设语气用法]（如果沒有…的话）

　　 Were it not for you, I would lose my way.

　　5. The + 比较级…, the + 比较级…（越…，就越…）

　　The harder you work, the more you gain.

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