An organic compound " P " of molecular formula $\mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_3$ gives positive Iodoform test but negative Tollen's test. When " P " is treated with dilute acid, it produces " Q ". " Q " gives positive Tollen's test and also iodoform test. The structure of " P " is :

$$ \text { Identify A in the following reaction. } $$

Choose the correct option for structures of $A$ and $B$, respectively