The boy began to play chess at the age of three.（改为同义句） The boy began to play chess ____ ___
问题描述：
The boy began to play chess at the age of three.（改为同义句） The boy began to play chess ____ ___
The boy began to play chess at the age of three.（改为同义句）
The boy began to play chess ____ ____ ____ ____ ____ ____.
答
when he was three years old.