When Peter Sanger and Liang Wu got together, it    1    （strike）them that they must be long-lost friends, Both firm advocates in the fight    2    air pollution, they believe that if you can't measure it, you can't beat it. That's    3     they founded Green City Solutions: "The solution to quantifiably improve city air."

The invention—the City Tree—act as an air purifier-an interesting    4    （add）to urban trees and green spaces. Rooted in science, air pollution can be eaten by the vertical flat-paneled（平面的）"trees"    5    （dot）around cities across Europe, while the "trees" also act as seats for pedestrians Sanger and Wu's vision is for a world in which people in cities can live    6    （healthy）. They long to create living conditions that allow all people around the world to permanently have cleaner air    7    （breathe）.

Using remote technology, the City Tree combines    8    air-purifying feature of moss with remote technology to increase the air flow through the "trees". This allows them to "suck up" and clean more air than normal, and the amount they filter can be increased    9    （depend）on pollution levels at different times of day.

The German green-tech start-up is now funded by the European Commission to set up a City Tree network of 15 brand new units and test it in a    10    （science）way in Berlin's pollution hotspots next year.