问题

Mr. Smith has ____ daughter who has won two national painting prizes.
A:a 8-year-old
B:an 8-year-old
C:a 8-years-old
D:an 8-year-olds;
B:an 8-year-old
C:a 8-years-old
D:an 8-year-olds;
正确答案是: