a champion at singing的用法和样例：
- He is a champion at writing familiar essays.
- He became a champion at last in virtue of his perseverance.
- Become a champion at minimizing the work you take home for the weekend. Leave enough time to recharge your battery.
- I draw the line at singing a solo in public. I'll tell jokes but I won't sing.
- It's a civic pride to have a champion.