$3$-Phenylpropene reacts with $\mathrm{HBr}$ in the presence of peroxide, the major product formed

Observe the following reactions and predict the nature of $\mathrm{A}$ and $\mathrm{B}$ 

$\mathrm{B}\underset{\mathrm{hv}}{\overset{\mathrm{HBr}}{\leftarrow }}$  $\stackrel{\mathrm{HBr}}{\to }\mathrm{A}$

$2,3$-Dimethyl-$2$-butene can be prepared by heated which of the following compounds with a strong acid?

Acid-catalysed hydration of alkenes except ethene leads to the formation of

$2$-Phenylpropene on acidic hydration gives