Explanation:

Correct Answer is (b).Enact means to make law/applicable by law.
Privilege means a special right or advantage.
Demonstrate means to show.
The sentence talks about how the enactment of both taxes i.e. STT and LTCG will result in customers preferring short-term stocks over long term ones.
The only word that suits the blank is “privilege” as seen from the meaning given above.
Hence option B is correct.