Answer : 4. "Solution to plastic pollution"
Explanation :

World Environment Day is the biggest international day for the environment. Led by the United Nations Environment Program (UNEP), and held annually since 1973, it has become the largest global forum for environmental outreach. It is celebrated by millions of people across the world.

World Environment Day 2023 is hosted by Côte d'Ivoire and supported by the Netherlands and the theme will focus on solutions to plastic pollution under the #BeatPlasticPollution campaign. It's a reminder that people's action on plastic pollution matters. The steps governments and businesses are taking to tackle plastic pollution are a result of this action.

- Host: Côte d'Ivoire in partnership with the Netherlands

- Theme: Solution to plastic pollution