定冠词的用法
1.用在姓氏复数前，表示一家人 。The Greens are at table.
2.用在年代、朝代名词前或用在世纪或逢10的`复数年代前。( 在某人50多岁时用in ones 50s)
A great many important events took place in the 1900s.
The Tang Dynasty(唐朝).
3 .用在表示计量单位的名词前。 Apples are sold by the kilogram.
但如果是单位名词的总称，名词前不用冠词，如：
by weight; by time; by length
Fruit is sold by weight.
4.特指双方都明白的人或者事物。 Take the medicine.
5.指上文提到过的人或者事物。 He bought a house. I’ve been to the house.
the sun, the Internet, the moon，但space前没有冠词
7.与形容词或分词连用，表示一类人或者一类事物。
the rich, the wounded, the new.
8.用在表示乐器的名词前，但中国乐器前没有定冠词 play the piano, play erhu
9.用在序数词、形容词最高级以及形容词only, very, same前面 。
She is always the first to come and the last to leave.
10.动词+sb.+介词+the +身体的某一部位
take sb. by the arm抓住某人的手臂hit sb. in the face打某人的脸
11.用在the more…,the more…结构中，表示“越……越……”(more指形容词的比较级)
The harder you study, the better you will learn.
12.用在发明物的单数名词前，既表示特指又表示类别。
Bell invented the telephone in 1876.
13.固定短语
on the whole, in the way, go to the theatre/cinema, to tell the truth, all over the world, in the distance, in the form of