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Answer:
A
Step-by-step explanation:
We can see from the conditions of the reaction that the incoming nucleophile is -SCH3 and there are two possible leaving groups in the substrate.
First of all, we have to look at the conditions of the reaction. We can see that the reaction is taking place in DMF, a polar aprotoc solvent. This condition favours the SN2 synchronous mechanism over the SN1 ionic mechanism.
Hence, the nucleophile at the 1-position is preferentially substituted owing to the conditions of the reaction.
Thus, option A is the major product of the reaction.