Lactose is made of . . . . . . .

• A
  $α-D$-glucose and $β-D$-fructose
• B
  $α-D$-glucose and $β-D$-galactose
• C
  $β-D$-galactose and $β-D$-glucose
• D
  $α-D$-glucose and $α-D$-glucose