Lactose is a disaccharide of

• A
  $\alpha-D$-glucose and $\alpha-D$-fructose
• B
  $\beta-D$-glucose and $\beta-D$-galactose
• C
  $\alpha-D$-glucose and $\beta-D$-ribose
• D
  $\alpha-D$-glucose and $\beta-D$-galactose