Which one of the following sets of monosaccharides forms sucrose?

• A
  $\alpha-D$-glucopyranose and $\beta-D$-fructofuranose
• B
  $\alpha-D$-glucopyranose and $\alpha-D$-fructofuranose
• C
  $\beta-D$-glucopyranose and $\alpha-D$-fructofuranose
• D
  $\alpha-D$-glucopyranose and $\beta-D$-fructopyranose