A hydrocarbon `A` of the molecular formula `C_8 H_10`. On ozonolysis gives only the compound `B(C_4 H_6 O_2)`. The compound `B` can also be obtained from the alkyl bromide `C(C_3 H_5 Br)` upon treatment with `Mg` in dry ether followed by the addition of `CO_2` and acidification. Identify `A, B` and `C` and also give equations for the reactions.