Complete the following `:`
`a.`
`b.`

Explanation

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.