Who is the biggest environment activist?0 pointsGreta ThunbergLeah ThomasAyana Elizabeth JohnsonDavid Attenborough

The biggest environment activist is subjective and can vary based on different criteria such as influence, reach, or specific environmental causes. However, all four individuals listed have made significant contributions to environmental activism:

1. Greta Thunberg: A Swedish environmental activist who gained international recognition for promoting the view that humanity is facing an existential crisis arising from climate change. Thunberg is known for her straightforward speaking manner and for her youth.

2. Leah Thomas: An intersectional environmental activist and eco-communicator based in Southern California. She's the founder of The Intersectional Environmentalist platform which explores the intersections of social and environmental justice.

3. Ayana Elizabeth Johnson: A marine biologist, policy expert, writer, and Brooklyn native. She is founder of Urban Ocean Lab, a think tank for coastal cities, and is co-creator and co-host of the Spotify/Gimlet podcast "How to Save a Planet."

4. David Attenborough: A broadcaster and natural historian. He is best known for writing and presenting, in conjunction with the BBC Natural History Unit, the nine natural history documentary series forming the Life collection that together constitute a comprehensive survey of animal and plant life on Earth.

Each of these activists has a different approach and focus, making it difficult to determine who is the "biggest" environmental activist. It would depend on how one defines "biggest" - whether it's by influence, reach, or some other measure.