Define "reducing sugar." $($b$)$ Show the reaction product of glucose after it is used as a reducing sugar. $($c$)$ Explain why fructose is also considered a reducing sugar. $($Hint: It must first undergo a chemical conversion.$)($d$)$ Sucrose is a disaccharide composed of glucose and fructose $($Glc$(12)$Fru$).$ Explain why sucrose is not a reducing sugar, even though both glucose and fructose are.