Life is not easy in senior high school. You've got the pressure of studies and exams. From time to time, you may feel depressed and frustrated. When depression strikes, you have to take measures to fight it. One of the strangest ways to fight depression is to eat salt, scientists have found. Salt acts as a natural anti-depressant  , researchers say. While too much can lead to high blood pressure and heart disease, not enough can cause "psychological  depressions", a study has reported. The study, by researchers at the University of Iowa in the US, discovered that when rats are _ in salt, they don't do activities they normally enjoy. The recommended daily salt intake for an adult is four grams, although experts say the body needs only half as much. However, most adults in the developed world consume around ten grams a day, mainly because their diets contain high salt amounts. Today, 77 percent of US salt intake comes from processed and restaurant foods, like frozen dinners and fast food. The minerals in salt are required by the body--in small quantities--to help move liquid in and out of cells. But too much can cause diseases, for example high blood pressure. Today scientists are finding that salt is an addictive substance--almost like a drug. One sign of addiction is using a substance even when it's known to be harmful. Many people are told to eat less salt due to health concerns, but they have trouble doing so because they like the taste and find low-salt foods tasteless. Humans have a long history of eating salt. In the Stone Age, people didn't need to find salt, because they hunted most of their food, and ate a lot of red meat, which has plenty of salt in it. But when people began to farm, about 10,000 BC, they started to eat mainly grains like rice and wheat, and very little meat. Then they had to find another way to get salt. Which of the following statements is true?
People have trouble reducing salt because they don't know it is harmful toeat too much of it. Before 10,000 BC, human beings did not need salt. The richer the country is, the more salt is eaten there. Taking more than 4 grams of salt a day can be harmful for an adult's health.