Passage One

Salt is a principal wicked substance. Salt, sodium chloride (氯化钠), 40 percent of which is sodium (钠), is an element essential to human body. But sodium also boosts blood pressure. It makes the body retain fluids; greater fluid retention increases total blood volume, and this increase raises blood pressure. Where salt is used freely, a large proportion of the population develops chronic high blood pressure, which is a primary factor in heart disease and stroke. Farmers in northern Japan traditionally preserve their food with salt. They consume as much as six teaspoons a day-and 40 percent of them have high blood pressure. Among the Eskimos. of Greenland, however, who consume little salt, high blood pressure is almost unheard of. The body of an needs only about 200 milligrams of sodium a day -- the amount in 500 milligrams, or 1/10 of teaspoon, of salt. But the average American consumes about 12,000 milligrams, or more than two teaspoons, of salt a day -- which supplies 24 times as much sodium as necessary; Germans consume an average 5,300 milligrams of salt a day. A sharp reduction is recommended by authorities everywhere -- to about 8,000 milligrams of salt per day for healthy people. For those who already suffer from high blood pressure, the normally suggested maximum is about 2,000 milligrams per day; more drastic restrictions -- to about 200 milligrams -- are required in special cases. However, if this recommendation is adopted, food will become almost insufferably bland for most Americans and Europeans. So some physicians prescribe as a replacement seasoning potassium chloride (氯化钾), which tastes salty but contains no sodium. Meanwhile, it should also be taken into account that extremely heavy use of potassium -- unlikely because of its unpleasant taste in large doses -- can cause death. Hence, the substitution of one chloride for the other should be undertaken only on the advice of a doctor.

According to the passage, which of the following is NOT true about the function and nature of slat