Question

he is ______boy A. an eight years old B .an eight-year-old

Answer 1

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。

Answer 2

B
eight-year-old是复合形容词，就象：ten-year
work,
five-minute
walk，用作定语修饰后面的名词boy
an
eight-year-old
boy
=
a
boy
of
eight
(years
old)