Concept:The IUCN World Conservation Congress meets at a fixed periodic interval to set global conservation priorities.
Explanation:The IUCN World Conservation Congress is the world's largest biodiversity conservation forum.
It is held once every 4 years, meaning the gap between two sessions is exactly 4 years.
The Congress brings together governments, NGOs, scientists, and indigenous leaders from over 160 countries.
More than 10,000 delegates participate in each session.
During the Congress, members vote on hundreds of resolutions that shape IUCN Red List policies, protected areas, and species action plans.
The Congress also elects the 36-member IUCN Council and approves the strategic direction for the next four-year period.
A notable session was held in Marseille, France, in 2021, which addressed post-2020 biodiversity targets.
The next Congress is scheduled for 2025 in Abu Dhabi, UAE.
Since the Congress is convened at an interval of every 4 years, the correct option matches this interval.
Answer:4 years (Option D).