什么是 “5years”？
“5 years”（注意中间有空格）通常用于表示一段持续的时间长度，例如：
- I have lived here for 5 years.
- She studied French for 5 years.
这种结构一般出现在句子的状语部分，不能直接修饰名词。
什么是 “5–year–old”？
“5-year-old” 是一个复合形容词，用来描述某人或某物的年龄，必须用连字符连接，并且通常放在名词前作定语，例如：
- He is a 5-year-old boy.
- They adopted a 5-year-old dog.
注意：当单独使用时（不修饰名词），应写为 “5 years old”：
- He is 5 years old.
常见错误
❌ 错误：He is a 5 years old boy.
✅ 正确：He is a 5-year-old boy.
❌ 错误：I’ve worked here since 5-year-old.
✅ 正确：I’ve worked here for 5 years.
总结
| 表达形式 | 用途 | 示例 |
|---|---|---|
| 5 years | 表示时间段（作状语） | I waited for 5 years. |
| 5-year-old | 复合形容词（修饰名词） | a 5-year-old child |
| 5 years old | 表语结构（说明年龄） | She is 5 years old. |