a. Two `(-OH)` groups are on the same plane.
Therefore, reagent `I` or `II` can used.
b. Two` (-OH)` groups are on the opposite plane.
Therefore, any reagent `III` to `IV` can be used.
c. Two `(-OH)` groups are on the same plane. ltbr. Therefore, reagent `I` or `II` can be used.
