People in isolated rain-forest communities tend to live on a largely vegetarian diet, and they eat little salt. Few of them suffer from high blood pressure, and their blood pressure does not tend to increase with age, as is common in industrialized countries. Such people often do develop high blood pressure when they move to cities and adopt high-salt diets. Though suggestive, these facts do not establish salt as the culprit in high blood pressure, however, because__. Which of the following most logically completes the argument given below? ['it is possible to have a low-salt diet while living in a city in an industrialized country', 'genetic factors could account for the lack of increase of blood pressure with age among such people', 'there are changes in other aspects of diet when such people move to the city', 'salt is a necessity for human life, and death can occur when the body loses too much salt']