The correct answer is (b). Harisena composed the Mandsaur Prasasti.
The Mandsaur Prasasti is a Sanskrit inscription that was composed in the 7th century CE by Harisena, the court poet of the Gurjara-Pratihara king Yashovarman. The inscription is a eulogy to Yashovarman and his achievements. It is one of the most important sources of information about the Gurjara-Pratihara dynasty.
Vasul was a 6th-century CE Indian poet who is best known for his work, the Vasucarita. Vats Bhatti was a 7th-century CE Indian poet who is best known for his work, the Bhattikavya.
(a) Vasul is incorrect because Vasul was a 6th-century CE Indian poet who is best known for his work, the Vasucarita. The Mandsaur Prasasti was composed in the 7th century CE.
(c) Vats Bhatti is incorrect because Vats Bhatti was a 7th-century CE Indian poet who is best known for his work, the Bhattikavya. The Mandsaur Prasasti was composed by Harisena, not Vats Bhatti.
(d) None of the above is incorrect because Harisena composed the Mandsaur Prasasti.