The reaction proceeds via an electrophilic addition mechanism. The proton ($\text{H}^+$) from $\text{HBr}$ attacks the alkene double bond to form the most stable carbocation intermediate. Between the two possible carbocations, $\text{C}_6\text{H}_5\text{C}^+\text{HCH}_2\text{CH}_3$ (a benzylic secondary carbocation) is significantly more stable than $\text{C}_6\text{H}_5\text{CH}_2\text{C}^+\text{HCH}_3$ (a standard secondary carbocation) because of strong resonance stabilization from the adjacent phenyl ring. The bromide ion ($\text{Br}^-$) then attacks this stable benzylic carbocation to form 1-bromo-1-phenylpropane ($\text{C}_6\text{H}_5\text{CH(Br)CH}_2\text{CH}_3$) as the major product. Since the exact structural options are missing from the input text, the precise correct option cannot be visually verified.