Question

He is_boy. A.a seven-years-old B.an eight-year old C.the seven-year-old Dan eight-year-older理由

Answer 1

一个男孩、此处没有特指，所以用不定冠词seven和eight是首个音节不同，an后面加原音开头，即an和eight联用，a和seven联用几岁的在这里是一个结构，数字-year（不论数字是几，year绝对不能用复数形式）-old（必须是原级）这个结构相当于一个形容词，不用另外加修饰楼主B选项漏了一个连字符号答案应该是B：He is an eight-year-old boy

Answer 2

按说应该是an eight-year-old boy或a seven-year-old boy。连字符连接的合成形容词中名词用原形，形容词用原形。