. A. CIRCUMSTANCE B. SITUATION C. CASE D. FORMV/. READ THE FOLLOWIN...

50/. A. circumstance B. situation C. case D. formV/. Read the following passage and mark the letter A, B, C, or D to indicate the correct answerACID DUSTCalcite-containing dust particles blow into the air and combine with nitric acid in pollutedair from factories to form an entirely new particle-calcium nitrate. These nitrates have optical andchemical properties that are completely different from those of the originally dry dust particles.Due to this, climate models need to be updated to reflect this chemistry. Calcite dust is commonin arid areas such as Israel, where this past winter scientists collected particles for analysis.Working from a mountaintop, the team collected dust that had blown in from the northernshores of Egypt, Sinai, and southern Israel. The particles had combined with air containingpollutants that came from Cairo. They analyzed nearly 2,000 individual particles and observed thephysical and chemical changes at the W.R Wiley Environmental Molecular Sciences Laboratory.An important change in the properties of the newly formed nitrate particles is that theyabsorb water and retain moisture. These particles can scatter and absorb sunlight-presentingclimate modelers, who need to know where the energy is going, a new wild card to deal with.Other studies of dust samples from the Sahara and the Saudi Arabian coast and loess from Chinashow that the higher the calcium in the mineral, the more reactive they are with nitric acid. Infact, once the particle is changed, it stays that way.