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For about 100 years, scientists thought that peptic ulcers were caused by stress, spicy food, and alcohol. Later, researchers added stomach acid to the list of causes and began treating ulcers with antacids. Now it is known that peptic ulcers are predominantly caused by Helicobacter pylori, a spiral-shaped bacterium that normally exist in the stomach.
The ratio of hydrogen atoms to oxygen in water (H2O) is 2:1.
During the twentieth century, a variant of the metric system was used in Russia and France in which the base unit of mass was the tonne. Instead of kilograms, this system used millitonnes (mt).
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Blood is approximately twice as thick as water because of the cells and other components found in it.