Wild Chinese sturgeon(鲟) are thought to have lived at     1     same time as dinosaurs and among the first class of protected animals in China. Last week, a wild Chinese sturgeon, which is believed to be the     2     (large) ever found in the past two decades, arrived in Beijing for better treatment. The species is a     3     (serious) endangered fish species in China and can be found only in the Yangtze and Pearl rivers.

The Chinese sturgeon “Houfu”,     4       literally means “good fortune for ever after”, arrived at the Beijing Aquarium on Monday after 22 hours of transport from Hubei Province.

When the fish     5     (find) by a fisherman in the Yangtze River Basin, it had been suffering from multiple     6     (injury). It was sent to the Yangtze River Fisheries Research Institute for treatment immediately. As she was so weak, local care takers had difficulty     7     (feed) it. The Yangtze River Fisheries Research Institute decided     8     (move) it to Beijing to receive further treatment.

Nicknamed “Aquatic giant pandas” and     9     (list) as a wild creature under state protection, the species has been struggling due to water projects, busy waterway traffic or pollution in recent years. The number of Chinese sturgeon living in the wilds has fallen sharply to about 50 now     10     about 1,000 in 1982, according to researchers’ estimates.

When Peter Sänger 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.”

Their invention — the City Tree — acts as an air purifier — an interesting     4     (add) to urban trees and green spaces. Rooted in science, air pollution can     5     (eat) by the vertical flat-paneled (平面的) “trees” dotted around cities across Europe, while the “trees” also act as seats for pedestrians. Sänger 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 CityTree 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 CityTree network of 15 brand new units and test it in a     10     (science) way in Berlin's pollution hotspots next year.