The Siege of Damascus occurred on:

This question asks for the specific date of a historical event, the Siege of Damascus, which was a pivotal moment in early Islamic history. The correct answer is 21 August 0634.

• The Siege of Damascus was a significant event during the Muslim conquest of Syria. The city of Damascus, then part of the Byzantine Empire, fell to the Rashidun Caliphate army under the command of Khalid ibn al-Walid on August 21, 634 CE. This victory was crucial for the expansion of the early Islamic empire.
• The dates 15 March 0634 and 10 December 0634 are incorrect for the conclusion of the siege. While the siege itself lasted for some time, the fall of the city is historically recorded as August 21st. Therefore, 'None of these' is also incorrect as one option is accurate.