Explanation:

4th option is incorrect i.e. Panchasidhantika by Varahmihira is not a work on Grammar.
Varahamitra's main work is the book Pancasiddhantika on the Five dated ca. 575 CE gives us information about older Indian texts which are now lost. The work is a treatise on mathematical astronomy and it summarises five earlier astronomical treatises, namely the Surya Siddhanta, Romaka Siddhanta, Paulisa Siddhanta, Vasishtha Siddhanta and Paitamaha Siddhanta. It is a compendium of Vedanga Jyotisha as well as Hellenistic astronomy.