my son's two-year-old 和 my son's two year old 的不同之处？
老师，请问有连字符的组合词（连字符这个杆是不可以省略吗）的词组（或短语）通常作什么成分，是否所有有杆组合的词组（或短语都是有名词或形容词性词特质？
除形容词外，还有什么词性词组有杆词汇的组合吗？
有的连字符的词组（或短语）这杆能省略不？
two-year-old是作前置定语的形容词形式，也可以是名词。不可以作表语。因此你的第一个句子用其做表语是错的。第二个句子表语应为two years old.
two-year-old作名词时，复数形式为two-year-olds。
My two-year-old son is very clever.
There are several two-year-olds in the daycare centre.
复合名词带连字符、不带连字符还是直接拼写在一块主要由习惯决定。最好的方法还是查词典。如basketball, papar tiger, pencil-box
复合形容词由连字符连接最容易见到于作者自己临时杜撰的形容词. 如 He wrote to his friend in good-good-study English.
