While we were crossing the street, the policeman signed for us to stop.是什么意思？

While we were crossing the street, the policeman signed for us to stop.

我们正横穿马路时, 警察做手势叫我们停住。

while

conj. 在…期间，与…同时，虽然，

例句
A Dr Matthew Owens was reported missing while on an expedition to north-eastern Turkey.
据报道，一位叫马修·欧文斯的博士在前往土耳其东北部考察的途中失踪了。

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

were

be的过去时复数和第二人称单数形式，有时代替 was,用于条件从句、动词 wish 之后等；

例句
Shops, houses, and vehicles were set ablaze.
店铺、房子和车辆全都陷于火海。

crossing

n. 人行横道，十字路口，交叉，相交，横越，渡口；v. 交叉(cross的现在分词)；

例句
...the fastest crossing of the Atlantic by a commercial passenger vessel.
商用客船最快的一次横渡大西洋

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。

street

n. 大街，街道；

例句
On the far side of the street was a restaurant that looked acceptable...
远处街边有一家饭店看起来还可以。

policeman

n. （男）警察，警员，看守矿井的人，[化] 淀帚；

例句
A policeman has been shot dead in an ambush.
一次伏击中一名警察中弹身亡。

signed

adj. 有符号的，有正负之分的；

例句
The two countries signed an agreement to jointly launch satellites.
两国曾签订了联合发射人造卫星的协议。

for

prep. 为，为了，倾向于，关于，当作；conj. 因为，由于；

例句
I've come looking for a bit of advice.
我特来讨教。

us

pron. 我们；

例句
Shakespeare has accustomed us to a mixture of humor and tragedy in the same play.
莎士比亚让我们习见了同一场戏目中的悲喜交错。

to

prep. 向，朝着，到，关于，属于；adv. 朝一个方向的，到某种状态，关闭；

例句
I suggest you leave it to an expert...
我建议你把它留给专家来解决。

stop

vi. 停止，中断，逗留，（使）停止工作；vt. 塞住，堵塞，阻挠，止付；n. 停止，（管风琴的）音栓，停车站，（管风琴的）音管；

例句
Wine is radioactive but few people stop drinking it on that account.
酒是有放射性的，可是很少有人因此而戒酒。