Emperor Xuanzong was amazed , and he had his chancellor Zhang Shuo test Liu 's knowledge .
When Emperor Xuanzong offered sacrifices at Mount Tai in 725 , Liu Yan , then a child , wrote a song and submitted it to Emperor Xuanzong .
Emperor Xuanzong Emperor Xuanzong was amazed , and Xuanzong had Xuanzong 's chancellor Zhang Shuo test Liu 's knowledge .
When Emperor Xuanzong offered sacrifices at Mount Tai in 725 , Liu Yan , then a child , wrote a song and submitted it to Emperor Xuanzong .