Let's check the themes for the given years: i. 2023: "Solutions to Plastic Pollution" (with the campaign "Beat Plastic Pollution"). This is correct. ii. 2022: "Only one Earth". This theme marked the 50th anniversary of the 1972 Stockholm Conference, which had the same theme. This is correct. iii. 2021: "Ecosystem Restoration" (with the launch of the UN Decade on Ecosystem Restoration). This is correct. iv. 2020: "Time for Environment". The theme for World Environment Day 2020 was "Biodiversity", with the slogan "Time for Nature". "Time for Environment" is not the official theme. This pair is incorrect.