几年之后，那些山上也将栽满了树。
in a few years’ time意思是“几年时间之后”，类似的用法还有：In two days’ time, in three months’ time等。例如：
In two days’ time, the work will be finished.
两天的时间，就能完成此项工作。
11. Was it difficult to work on the Great Green Wall?
从事绿色长城工作难吗？
It + is / was + 形容词 + 不定式。这种句型中不定式是真正的主语，it是形式主语。例如：
It’s best to plant trees in spring.
最好在春季植树。
It’s best to read English every day.
最好每天读英语。
It’s interesting to play games with Children.
和孩子们一起做游戏是很有趣的。
12. But thanks to the Great Green Wall, the land produces more crops.
但是幸亏有绿色长城，土地长出了更多的庄稼。
thanks to幸亏，由于。thanks为名词，常用复数。例如：
Thanks to your help, we were successful. Thanks to the policeman, the old man was brought home.
由于你的帮助，我们成功了。多亏了警察，老人被送回了家。
13. The Great Green Wall is 7, 000 kilometres long, and between 400 and 1, 700 kilometres wide.
绿色长城有7000公里长，400到1700公里宽。
（1）计量的表达法是：
主语+ be+数词+metres / kilometers + long/ wide/ high/ tall/ deep等形容词。例如：
The river is about 100 metres deep. The mountain is nearly 4, 000 kilometres high.
这条河大约有100米深。这座山有近4000米高。
Our classroom is ten metres long and seven metres wide.
我们的教室十米长，七米宽。
（2）分数表达法：分子用基数词计数，分母用序数词计数，同时分子是1以上的数字，分母用复数形式；分子为1时，分母采用单数形式。l/2:one second; l/3:a third; 2/5:two fifths等。特殊的表达法有：a half, a quarter, three quarters等。
《Planting trees(第2页)》出自：www.89xue.com网www.89xue.com 14. — Is it straight?
— More or less!
— 它直吗？
— 有一点儿直!
more or less“差不多；大概”相当于about。
The road is two hundred metres long, more or less.
这条路大概有两百米长。
The exercises are more or less finished.
作业快要做完了。
15. Children under 1.2m in height can not be taken into the concert hall.
1.2米以下的孩子禁止带入会场。
height 为名词，形容词为high. 1.2 m in height 意为 1.2m high。如：
— What is his height？
— He is six feet in height (＝He is six feet high．)
— 他有多高？
— 他有六英尺高。
关于含有情态动词的被动语态的讲解
※含有情态动词的被动语态的构成
前两个单元已学过一般现在时态和一般过去时态的被动语态的构成，以及被动语态的用法。本单元学习含有情态动词的被动语态。它的构成形式是：情态动词+ be + 动词的过去分词；否定式是在情态动词后 + not, 疑问式是将情态动词放于主语之前。情态动词有：can, may, must, school, could, have to等。例如：We must find out the truth . → The truth must be found out .
（1）The trees must be planted in spring.
树必须春天栽。
（2）May the exercises be done tomorrow?
练习可以明天做吗？
（3）Books can not be taken out of the reading-room.
书不能带出阅览室。
（4）These young trees should be watered every day.
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