Correct Option: D

Dara Shikoh's spiritual quest or monotheistic strands in Hindu philosophy was a continuous process. This led him to study the Upanishads and with the help of some scholars of Banaras, he translated 50 Upanishads from Sanskrit to Persian. The text he prepared, the Sirr-I-Akbar, 'the Great Secret' was completed in 1657. He was of the firm opinion that the 'Great Secret' of the Upanishads is the monotheistic message, which is identical to that on which the Quran is based.