Introduction:
The Indus Valley Civilization, also known as the Harappan civilization, flourished around 2600 to 1900 BCE in the region that is now modern-day Pakistan and northwest India. It was one of the world's earliest urban civilizations, known for its advanced urban planning, trade networks, and sophisticated culture. One of the significant aspects of the Indus Valley Civilization was its trade relations with other contemporary civilizations, including Mesopotamia.

Explanation:
The statement that cloth was exported from the Indus Valley to Mesopotamia is based on multiple pieces of evidence. Let's examine each option to understand why option 'A' is the correct answer.

Option A: Piece of cotton fabric with an imprint of Harappan seal found in Sumer:
- Sumer was one of the earliest civilizations in Mesopotamia, known for its advanced agriculture, trade, and writing system.
- The discovery of a piece of cotton fabric with an imprint of a Harappan seal in Sumer indicates the presence of Indus Valley cloth in Mesopotamia.
- This finding suggests that there was a direct trade connection between the two civilizations, with the Indus Valley exporting cloth to Mesopotamia.

Option B: Reference to cotton in Sumerian sources:
- The reference to cotton in Sumerian sources is significant evidence supporting the trade of cloth between the Indus Valley and Mesopotamia.
- Sumerian texts mention the importation of "white gold," which is believed to refer to cotton, from the land of Meluhha, identified as the Indus Valley.
- These references indicate that cotton, a raw material for cloth production, was traded from the Indus Valley to Mesopotamia.

Option C: Piece of cotton fabric with Harappan seal at Bahrein:
- The presence of a piece of cotton fabric with a Harappan seal at Bahrein, an ancient trading hub in the Persian Gulf, suggests that Indus Valley cloth reached distant regions through trade networks.
- While Bahrein was not directly in Mesopotamia, it was a crucial intermediary for trade between the Indus Valley and Mesopotamia, making the presence of the fabric there indicative of its export to Mesopotamia.

Option D: Piece of cotton with Harappan seal found at Lothal:
- Lothal was a major Indus Valley city and a significant port.
- The discovery of cotton with a Harappan seal at Lothal indicates the production and export of cotton-based cloth from the Indus Valley.
- While Lothal was not directly in Mesopotamia, it served as a crucial trade link between the Indus Valley and other regions, including Mesopotamia.

Conclusion:
Based on the evidence presented, option 'A' is the correct answer. The discovery of a piece of cotton fabric with an imprint of a Harappan seal in Sumer provides direct evidence of cloth being exported from the Indus Valley to Mesopotamia. Additionally, references to cotton in Sumerian sources, the presence of cotton fabric with Harappan seals at Bahrein, and the discovery of cotton with Harappan seals at Lothal further support this trade connection. These findings highlight the significance of the Indus Valley Civilization's trade relations and the export of