Correct Answer - C
The Fischer projection of `(I) and (II)` is wrong because the functional group is not at the top. On rotating `(I) and (II)` by `180^(@)`. They are represented as shown:
Now, compare I,II,III, and IV
`(I) and (III)implies` Enantiomers
`(II) and (IV)implies` Identical or same
Therefore, the pairs of diastereomers are:
`(I), (II), (I), (IV)` , and `(II), (III)`
But the answer given is `(C ) (I, II)`.