填空题 Lackner, a {{U}} {{U}} 1 {{/U}} {{/U}}energy expert at Columbia University, has designed an {{U}} {{U}} 2 {{/U}} {{/U}}tree that soaks up carbon dioxide from the air using "leaves" 1,000 times more efficient than true leaves. He explains: The leaves are {{U}} {{U}} 3 {{/U}} {{/U}}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 {{U}} {{U}} 4 {{/U}} {{/U}}in water {{U}} {{U}} 5 {{/U}} {{/U}}and can dry naturally in the wind, soaking up more carbon dioxide.
He {{U}} {{U}} 6 {{/U}} {{/U}}that our total {{U}} {{U}} 7 {{/U}} {{/U}}could be removed with 100 million trees. The removed carbon dioxide can be {{U}} {{U}} 8 {{/U}} {{/U}}and stored; however, there isn't enough space to store it. But {{U}} {{U}} 9 {{/U}} {{/U}}are coming up with {{U}} {{U}} 10 {{/U}} {{/U}}, for example, peridotite, which is a great {{U}} {{U}} 11 {{/U}} {{/U}}of carbon dioxide. Another {{U}} {{U}} 12 {{/U}} {{/U}}could be the basalt rock {{U}} {{U}} 13 {{/U}} {{/U}}, which contain {{U}} {{U}} 14 {{/U}} {{/U}}gas bubbles. {{U}} {{U}} 15 {{/U}} {{/U}}carbon dioxide into these bubbles causes it to form {{U}} {{U}} 16 {{/U}} {{/U}}limestone. However, Lackner thinks the gas is very useful and it can be used to make {{U}} {{U}} 17 {{/U}} {{/U}}fuels for transport {{U}} {{U}} 18 {{/U}} {{/U}}. We have the technology to suck carbon dioxide out of the air, and keep it out, but whether it is economically {{U}} {{U}} 19 {{/U}} {{/U}}is a different question. We have to decide whether the cost of the technology is socially and economically {{U}} {{U}} 20 {{/U}} {{/U}}the price.