They live on the mountain tops where there's little soil,它们生长在土壤不多的山顶上

live on在...生活

I live on the same street as Peter.

我和彼得住在同一条街上。

They are asked to live on campus.

校方要求他们住校。

Occasional morning mists sweep across the high ground.这里偶尔会飘过晨雾

sweep across席卷，横扫；冲过，迅速掠过

Storms sweep across it and pile up great waves.

风暴袭来会激起巨大的海浪。

The reform bandwagon swept across the country.

改革浪潮席卷全国。

Water is so precious that the tree cannot afford to waste any.这里的水分太珍贵一丁点都不能浪费

afford to付得起, 能承担

We can afford to overlook minor offences.

我们可以不计较小过。

I can't afford to spend any more on food.

用在食物上的钱，再多一点儿我也花不起了。