Explanation:

The Bhagirathi is one of the two main headstreams of the Ganga (Ganges) River, considered sacred in Hinduism. Its origin is a significant geographical and cultural point. \nOption (A) Siachen Glacier: The Siachen Glacier is located in the eastern Karakoram range in the Himalayas, at an average altitude of $5,753 \text{ m}$ above sea level. It is the second-longest glacier in the world's non-polar areas. Rivers like the Nubra originate from this glacier, but not the Bhagirathi. Therefore, this option is incorrect. \nOption (B) Gangotri Glacier: The Bhagirathi River originates from the Gaumukh (meaning 'cow's mouth') snout of the Gangotri Glacier. The Gangotri Glacier is located in the Uttarkashi district of Uttarakhand, India, in the Garhwal Himalayas. It is one of the largest glaciers in the Himalayas and a primary source of the Ganga River system. Therefore, this option is correct. \nOption (C) Milam Glacier: The Milam Glacier is located in the Pithoragarh district of Uttarakhand, India. It is a major source of the Goriganga River, which is a tributary of the Kali River. The Bhagirathi does not originate from the Milam Glacier. Therefore, this option is incorrect. \nOption (D) Sona Glacier: There is no prominent glacier named 'Sona Glacier' that is widely recognized as the source of a major river like the Bhagirathi. It is not a known source for any significant river in the Indian subcontinent. Therefore, this option is incorrect. \nThus, the Bhagirathi originates specifically from the Gangotri Glacier at Gaumukh.