He won a gold medal in the Olympic Games,but he was just-----then A,at the age of 17 yeaesB,a 17-years-old boy C,a boy of 17 D,a 17-year boy 为什么选C

He won a gold medal in the Olympic Games,but he was just-----then A,at the age of 17 yeaesB,a 17-years-old boy C,a boy of 17 D,a 17-year boy 为什么选C
He won a gold medal in the Olympic Games,but he was just-----then A,at the age of 17 yeaes
B,a 17-years-old boy C,a boy of 17 D,a 17-year boy 为什么选C

He won a gold medal in the Olympic Games,but he was just-----then A,at the age of 17 yeaesB,a 17-years-old boy C,a boy of 17 D,a 17-year boy 为什么选C
a改成at the age of 17 就对了
B改为：a 17-year-old boy就对了
d:改：a 17 years old boy就对了