Read the following article and answer the question. Article: Breakthroughs in science and technology are paving the way for modern cities to support bigger populations. Now, we see the most exciting urban innovations to show you exactly how they'll improve your city's infrastructure . Lighting Up The Night Anthony Di Mari dreamed up an electric tree to help irrigate public parks and light them at night. These electric trees contain a special infill that collects water from rainfall. The water is then distributed through a shallow underground irrigation system with the help from the trees' swaying movement. An electric motor turns energy from the waving of the artificial trees into electricity, which is used to light up the trees' outer LEDs. Thinking Outside The Box As more people flock to urban areas, city planners will need to get increasingly creative about how to satisfy residents' health and transportation needs within decreasing available space. One way to achieve this is by updating infrastructure to support biking and walking by building suspended roundabouts like hovering in the Netherlands. By lifting bicycle and pedestrian traffic above busy roadways, cities can significantly decrease over-crowded traffic condition. Waving Hello To Clean Energy Cities that don't receive enough sunlight may find an attractive alternative in wave power. Since ocean waves rarely experience disruption , electric engines driven by their clockwork push-and-pull can reliably provide power throughout the year. Further, thanks to advances in wave power technology, engineers have been able to move wave power engines farther offshore, where the waves pack the most punch, making the engines extremely efficient. So in the future, heavily populated coastal cities may use wave to meet their energy needs. Question: What is the special infill used to do? Answer:
Answer:
To collect water from rainfall.