英语单词在什么情况下才加定冠词?（什么样的词）

定冠词也出现在其他 11 种情况中,非同时注意不可.
⑴用在单数名词前面,以代表同类的人或物,如：
● The ox is a useful animal for farmers.
● This type of work is easier for the teacher than for the student.
但当涉及 man 和 woman 这两个名词时,一般上不必用 the ：
● Man is mortal.
● Woman differs from man in many ways.
⑵用在单数名词前面来表示有关名词的抽象概念,如：
● Don't play the fool.
● Peter is fond of the bottle.
⑶用在数目字前面,如：
● Mr Li is somewhere in the 30s.
● She was not yet born in the 50s.
⑷用在测量单位前面,以表示“每”（each/per）,如：
● Some factory workers are paid by the hour.
● This car usually does 15 kilometres to the litre.
⑸用在比较级形容词或副词之前,以加强其意义,如：
● The teacher explained the idea again, but his students were none the wiser.
● Your mind will function all the better if you have some time away from your work.
⑹用在“the more/better...the more/better...”结构里,如：
● The more we practise, the more we improve.
● The better the staff, the better the performance.
⑺用在乐器名称之前,如：
● The piano sounds better than the organ.
⑻用在剧院、电影院之前,如：
● Do you often go to the cinema?
● Tom went to the Lido last week.
⑼用在四个方向之前,如：
● The sun rises in the east and sets in the west.
⑽用在复数姓氏之前,以表示有关家人,如：
● The Browns will visit us tonight.
⑾用在某些惯用语之前,如：
● We know the ins and outs of the matter.
● Compare the pros and cons before you make your decision.