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Vehicle pollution is a big problem especially in big cities. Still, more and more people are buying cars and keep using them. Have you heard about any interesting projects that [are help|will help|would helping|helps] to make people use vehicles less often?

Jody Xiong, together with the Chinese Environmental Protection Society, came up with such a project. The aim of his idea was to demonstrate the advantage of [walk|to walk|walked|walking] over using transport in the city. A large image was painted on a pedestrian crossing in Shanghai. It was a trunk of a tree without leaves. A rug with special paint was [laid|lied|lain|lay] on the sidewalk. A pedestrian stepped on a rug, and the soles* of his boots were painted with the green paint. So when he continued crossing the road, green footprints [are left|were left|left|were leave] on the tree. The more people stepped on the pedestrian crossing,[the most|more|the more|most] "leaves" the tree got. Would you like to add some "leaves" to make the tree greener?

*sole — the underside of footwear