New words：

necessary ['nesə.səri] adj. 必需的；必要的；必然的；无法避免的

Sample Sentences：

Oxygen is necessary for life.
It's necessary for us to study hard.
It may be necessary to buy a new one.
If necessary, we can always change the date of our trip.

New words：

soil [sɔil] n. 土壤；土地；国土；领土

Sample Sentences：

He died on British soil.
That farm has a very rich soil.
She makes her living from the soil.
Some soils are not suitable for farming.
Press the soil flat with the back of a spade.

New words：

decade ['dekeid] n. 十年

Sample Sentences：

We've been married a decade.
Nine years plus one year equals a decade.
Prices have risen steadily during the past decade
It will be at least another decade before we know if he was right.

New words：

colleague ['kɔli:g] n. 同事；同行；同僚

Sample Sentences：

I had a colleague who died decades ago.
My colleague has broken off the habit of smoking.
We were friends and colleagues for more than 20 years.

decade ['dekeid] n. 十年

New words：

innocent ['inəsnt] adj. 无辜的；清白的；无罪的；无辜受害的；无知的, 天真纯洁的

Sample Sentences：

He insisted he was innocent.
He declared that he was innocent.
Don't be so innocent as to believe everything you hear.