50/. A. circumstance B. situation C. case D. form
V/. Read the following passage and mark the letter A, B, C, or D to indicate the correct answer
ACID DUST
Calcite-containing dust particles blow into the air and combine with nitric acid in polluted
air from factories to form an entirely new particle-calcium nitrate. These nitrates have optical and
chemical 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 common
in 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 northern
shores of Egypt, Sinai, and southern Israel. The particles had combined with air containing
pollutants that came from Cairo. They analyzed nearly 2,000 individual particles and observed the
physical 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 they
absorb water and retain moisture. These particles can scatter and absorb sunlight-presenting
climate 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 China
show that the higher the calcium in the mineral, the more reactive they are with nitric acid. In
fact, once the particle is changed, it stays that way.
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