问题

He is only _______ boy. He isn’t old enough to take care of himself.
A:a 8-year-old
B:an 8-year-old
C:a 8-years-old
D:an 8-years-old;
B:an 8-year-old
C:a 8-years-old
D:an 8-years-old;
正确答案是: