Molecular formula `C_(4)H_(4)O_(4)` can have various structures:
(i) a cyclic ester (A)
(i) a dibasic acid (B) that on heating is converted into acrylic acid.
(ii) a dibasic acid (C) that foms meso tartaric acid with alkaline `KMnO_(4)`.
(iv) a dibasic acid (D) that forms racemic mixture of tartaric acid with alkaline `KMnO_(4)`.
Assign structures to (A), (B), (C) and (D).
