Sorry that is incorrect!

The indwelling of the Holy Spirit is necessary for salvation and entering the kingdom of God. The Holy Spirit sanctifies by attesting to the reality of Believer's faith, brands the Believer as a property of God's, and guarantees his inheritance in the future completion of salvation (2 Cor 1:21-22; 5:5).

The correct answer is "b" - the Holy Spirit sanctifies by assuring the Believer of the indwelling presence of Jesus Christ (1 John 3:24).