To answer this question, we need to have knowledge of Hindu mythology and the story of Ramayana.
Option A) Janaka - This option is correct. Sita was indeed the daughter of King Janaka. According to the Ramayana, Sita was found by King Janaka while ploughing the land. He raised her as his own daughter.
Option B) Dasaratha - This option is incorrect. Dasaratha was the father of Lord Rama, not Sita.
Option C) Vibheeshana - This option is incorrect. Vibheeshana was the younger brother of Ravana and played a role in the Ramayana, but he was not the father of Sita.
Option D) Himavaan - This option is incorrect. Himavaan, also known as the Himalayas, is a mountain range and not a king.
The correct answer is A) Janaka. Sita was the daughter of King Janaka.