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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).
Human stomach acid is strong enough to dissolve small pieces of metal such as razor blades or staples.
Cancer has been around as long as humankind, but only in the second half of the twentieth century did the number of cancer cases explode.
Cyanide works by making the human body unable to use oxygen.
People who have myopia, or nearsightedness, are not able to see objects at a distance but only up close. It occurs when the cornea is either curved too steeply, the eye is too long, or both. This condition is progressive and worsens with time. More than 100 million people in the United States are nearsighted, but only 20% of those are born with the condition. Diet, eye exercise, drug therapy, and corrective lenses can all help manage nearsightedness.