How many international standards has ISO developed that relate to sustainability?

The correct choice indicates that ISO has developed over 21,000 international standards that relate to sustainability. This extensive body of work reflects ISO's commitment to providing frameworks and guidelines that assist organizations across various sectors in their sustainability efforts.

ISO standards encompass a wide range of topics, including environmental management, social responsibility, and sustainable development, offering a structured approach for organizations to improve their performance in these areas. This large number signifies the growing recognition of the importance of sustainability in global markets and the need for standardized practices to ensure consistency, reliability, and effectiveness in sustainability initiatives.

While the other options suggest significant figures, they do not capture the comprehensiveness of ISO's portfolio concerning sustainability-related standards. The vast array of over 21,000 standards highlights the organization's proactive role in addressing global challenges related to sustainability and supporting businesses, governments, and other entities in their quest to operate sustainably.