GRAMMAR. Read the sentences and choose the correct variant.
1. Baking soda is / is being a white crystalline powder (NaHCO 3 ) better known to
chemists as sodium bicarbonate.
2. At temperatures above 149 degrees Celsius baking soda is decomposing /
decomposes into sodium carbonate, water, and carbon dioxide.
3. The native chemical and physical properties of baking soda allow / allows to use
it in a wide range of applications, including cleaning, deodorizing, buffering, and
fire extinguishing.
4. People have started / started to use baking soda in air pollution control because
it absorbs sulfur dioxide and other acid gas emissions.
5. Baking soda has come / came from England and was first used in America
during colonial times.
6. In 1846, Austin Church, a Connecticut physician, and John Dwight, a farmer
from Massachusetts, had established / established a factory in New York to
manufacture baking soda.
7. At the second stage of making baking soda they put / has put the intermediate
soda ash solution into a centrifuge, which separates the liquid from the crystals.
8. The saturated sodium solution moved / had moved through the tower before they
have seen / saw that the centrifuge has been / was out of work.
9. Specialists usually manufacture / manufactured standard grades of sodium
bicarbonate to meet customers' specific requirements, and particle size is / are
the major determinant of grades.
10. Managers have agreed/ had agreed to buy a new carbonating tower before the
prices goes / went up.
