Dong Yuhui said: When the child does not study hard, tell him about the "duck law." Dong Yuhui said: When the child does not study hard, tell him about the "duck law." Dong Yuhui said: When the child does not study hard, tell him about the "duck law." Dong Yuhui said: When the child does not study hard, tell him about the "duck law." Dong Yuhui said: When the child does not study hard, tell him about the "duck law." Dong Yuhui said: When the child does not study hard, tell him about the "duck law." Dong Yuhui said: When the child does not study hard, tell him about the "duck law."