Haveyoueverwonderedwhybirdssing?Maybeyouthoughtthatthe...
问题详情： Haveyoueverwonderedwhybirdssing?Maybeyouthoughtthattheywerejusthappy.Afterall,youprobablysingorwhistlewhenyouarehappy. Somescientistsbelievethatbirdsdosingsomeofthetimejustbecausetheyarehap...