Option c is the correct answer. Chandragupta II assumed the throne after killing his elder brother Ramagupta, who was the designated successor of Samudragupta. Ramagupta was a weak and incompetent ruler who failed to protect his kingdom from the invasion of the Saka king Rudrasimha III. He agreed to surrender his wife Dhruvadevi to the Saka king as a ransom, but Chandragupta II intervened and killed both Ramagupta and Rudrasimha III in a daring coup. He then married Dhruvadevi and became the king of the Gupta Empire. This story is narrated in a Sanskrit political drama called Devichandraguptam, which was written by Vishakhadeva, who is generally identified with Vishakhadatta.