As we drove towards the desert, the vegetation became sparse.是什么意思？

As we drove towards the desert, the vegetation became sparse.

我们驱车前往沙漠，沿途的草木渐渐变得稀疏。

as

adv. 同样地，一样地，例如；prep. 作为，以…的身份，如

例句
As far as I can recall, Patti was a Smith.
我记得帕蒂是姓史密斯的。

we

pron. 我们，咱们，笔者，本人，朕，人们；

例句
...expensive make-up that we saw being advertised by a beautiful model...
我们所见的由一位漂亮模特代言的昂贵化妆品

drove

n. 人群 ，畜群；v. 驾驶（drive的过去式）；

例句
We drove east to Rostock, where my map led me astray.
我们驱车向东去罗斯托克，但地图却给我指错了方向。

towards

prep. 朝，向，对于，接近，为了；

例句
...absent fathers who fail to pay towards the costs of looking after their children.
那些不在子女身边、未能支付抚养费的父亲

the

art. 指已提到的人（物），指说话人与听者已知的人（物），用于独一无二的事物前，与形容词最高级和序数词连用；

例句
He did have a real knowledge of the country...
他对该国的确知之甚多。

desert

n. 沙漠，荒地，应得的赏罚，功劳，美德；adj. 沙漠的，荒芜的，不毛的，无人的；

例句
The army would try to hold the western desert with a bare minimum of forces...
军队会用尽可能少的兵力扼守西部的沙漠。

vegetation

n. 植物（总称），草木，[医]赘生物，增殖体，无所作为的生活，单调的生活，[植]营养体生长，发育；

例句
...bands of natural vegetation between strips of crops...
农作物狭地之间的野生植被带

became

v. 变为，成为（ become的过去式 ）；

例句
It became very clear that the incident was not just an aberration, it was not just a single incident.
事实已经很清楚，这件事不是偶发的，它并不是一起孤立的事件。

sparse

adj. 稀疏的，稀少的；

例句
Kangaroos compete with sheep and cattle for sparse supplies of food and water...
袋鼠与牛羊争夺稀少的食物和水。