The teacher is cleaning the blackboard with a board rubber.是什么意思？

The teacher is cleaning the blackboard with a board rubber.

老师正在用黑板擦擦黑板。

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。

teacher

n. 教师，教员，老师，先生，[航]教练机；

例句
He was now a teacher and a respectable member of the community.
他现在是一位教师，并且是社区内受人尊敬的一员。

is

vt.& vi. 是（be的三单形式；n. 存在；

例句
Bollinger 'RD' is a rare, highly prized wine.
博林格RD香槟是一种名贵的备受推崇的葡萄酒。

cleaning

n. 清洁，打扫，（家畜等的）胞衣；v. （使）清洁( clean的现在分词 )，变干净，除去…的灰尘，使…干净；

例句
The approved method of cleaning is industrial sand-blasting.
得到正式认可的清洁方法是工业喷砂清洗。

blackboard

n. 黑板；

例句
There was a blackboard with seven names chalked on it.
黑板上用粉笔写着7个人名。

with

prep. 和，跟，随着，关于，和…一致；

例句
A waiter entered with a tray...
侍者端着托盘进来了。

board

n. 板，董事会，甲板，膳食；vt. 上（船、车或飞机），收费供…膳宿，使搭伙，使寄宿，强行登（船）；vi. （火车、轮船、飞机等）接受乘客，搭伙，寄宿；

例句
The company had eight departures and 11 new arrivals on its management board in 1980-1989.
在1980至1989年间，公司管理委员会离职8人，新吸收11人。

rubber

n. 橡胶，橡皮，决胜局，避孕套；adj. 橡胶制成的；vt. 涂橡胶于，用橡胶制造；vi. 扭转脖子看，好奇地引颈而望；

例句
Seven people were wounded when soldiers fired rubber bullets to disperse crowds...
士兵发射橡皮子弹驱散人群时有7个人受了伤。