The 9th ministerial conference of the WTO, held during 3 December-6 December 2013, was concluded at:

The correct option is Bali, Indonesia.

Step-by-Step Explanation:

1. Background of the Conference: The World Trade Organization (WTO) holds its Ministerial Conference every two years, which serves as the topmost decision-making body of the organization.

2. The 9th Ministerial Conference (MC9): The 9th Ministerial Conference was held from 3 December to 6 December 2013 in Bali, Indonesia.

3. Key Outcome: The conference was historically significant because member nations agreed on the "Bali Package", which was the first major multilateral trade agreement successfully negotiated under the WTO since its creation in 1995. The package included measures aimed at trade facilitation, food security in developing nations, and cotton trade issues.