According to Box, a leading Greenland expert, tundra fires in 2012 from as far away as North America produced great amounts of soot, some (1) of it drifted over Greenland in giant plumes of smoke and then (2) fell as particles onto the ice sheet. Scientists have long known that soot particles facilitate melting by darkening snow and ice, limiting (3) it’s ability to reflect the Sun’s rays. As Box explains, “Soot is an extremely powerful light absorber. It settles over the ice and captures the Sun’s heat. ”The result is a self-reinforcing cycle. As the ice melts, the land and water under the ice become exposed, and since land and water are darker than snow, the surface absorbs even more heat, which (4) is related to the rising temperatures.
Which option best completes the sentence?
1.No change
2.falls
3.had fallen
4.will fall
help me, please