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Read this passage from NASA about preventing fractures in elderly people. Which topic sentence would be the best statement of the main idea?

Meals should be nutritionally balanced with calcium-rich foods (mild, small fish, etc.) and vitamin D (fish, mushrooms, etc.). Limited sunbathing is also important for activation of vitamin D. Physical exercise to increase bone load and muscle training should also be integrated into each person’s daily life. Those at high risk for fractures should take effective medicines to reduce the risk of fractures.


Astronauts have discovered that fractures can be prevented in low-gravity situations by eating vitamin D and staying out of the sun.


Elderly people can prevent bone loss and fractures by watching what they eat and exercising every day.


Nutrition is the most important element in preventing fractures in elderly people.


The three key elements for promoting the health of elderly people to prevent fractures are nutrition, exercise and medicine.