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In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.

Article: A woman wears a face mask to protect her from polluted air in prefix = st1 /Lanzhou,China, in December. A new study showed air pollution might put people more at risk for heart disease than scientists had thought. Kristin Miller, a doctoral student at the UniversityofWashington, said chances of getting the disease were related to not only which city a woman lived in, but also where in the city. The study found that the effects of air pollution were often larger within cities than between cities. The new findings make experts suspect that current pollution limits may be inadequate. Scientists examined rates of heart attack, stroke and other cardiovascular events in women with long-term exposure to air pollution. The study involved women over the age of fifty who had no sign of cardiovascular disease at the start of the research. The study followed the women for as long as nine years to see how they would develop cardiovascular problems. The researchers also examined levels of fine particles (,) in the air in 36 areas across the country. That information came from the Environmental Protection Agency. The extremely small particles came from industrial smoke and traffic, along with things like wood-burning fireplaces in houses. In the study, every ten-microgram increase in the risk of a cardiovascular event. But it was related to a seventy-six percent increase in the risk of death from cardiovascular disease. But just how do particles in the air damage the cardiovascular system? The particles may cause the lungs to swell and release chemicals from the pollutants into the blood. The chemicals then could damage the heart.
Answer: the relationship between air pollution and heart diseases
Output:
The passage mainly talks about _ .