用在特定的时间前,morning/afternoon/evening
指独一无二的事物,ex,the sun rise in the east.
用在特定的方位前,ex,She hopes to move to the south
用于形容词的最高级前,ex.this is the highest building in shanghai
用于序数词前Monday is the first day of the week.
用于单数名词前表示一类人或事物,the elephant is a very intelligent animal
用于乐器前she enjoys playing the piano in her free time.
用于姓氏复数前,表示一家人.We live next to the smiths.