问题

Little Tom is only ____ boy, however, he has already learned about 1,000 English words.
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: