复数
the old/young/rich/poor/blind/deaf 都是一类人，是复数，谓语动词用复数（are/ do)
1、the + adj.： 英语中，“the + 形容词”结构用来表示一类人，是复数。
如: the young， the educated， the middle-aged， the wise …
The old are well looked after in this old house.
The wounded are being tended in the hospital.
注：表示类别的还可用：a / an + 名词单数(属于单数)the + 名词单数(属于单数)
名词的复数(是复数)
如: A horse is a useful animal.
Students are persons who study at school.
The telephone was invented by a man called Bell.
注：表示发明物，用：the + 名词(单数
