填空题

Lackner, a 1 energy expert at Columbia University, has designed an 2 tree that soaks up carbon dioxide from the air using "leaves" 1,000 times more efficient than true leaves. He explains: The leaves are 3 in a resin that contains sodium carbonate, which pulls carbon dioxide out of the air and stores it as a bicarbonate on the leaves. To remove the carbon dioxide, the leaves are 4 in water 5 and can dry naturally in the wind, soaking up more carbon dioxide.
He 6 that our total 7 could be removed with 100 million trees. The removed carbon dioxide can be 8 and stored; however, there isn"t enough space to store it. But 9 are coming up with 10 , for example, peridotite, which is a great 11 of carbon dioxide. Another 12 could be the basalt rock 13 , which contain 14 gas bubbles. 15 carbon dioxide into these bubbles causes it to form 16 limestone. However, Lackner thinks the gas is very useful and it can be used to make 17 fuels for transport 18 . We have the technology to suck carbon dioxide out of the air, and keep it out, but whether it is economically 19 is a different question. We have to decide whether the cost of the technology is socially and economically 20 the price.