Heart attacks are most likely to occur on Mondays. The accepted explanation is that because Monday is the first day of the workweek, people feel more stress on Mondays than on other days. However, research shows that even unemployed retired people are more likely to have heart attacks on Mondays than on other days. Which one of the following, if true, most helps to explain the increased likelihood that an unemployed retiree will have a heart attack on a Monday? ['Because they associate Monday with work, retired people are more likely to begin large projects on Mondays.', 'Many retired people take up part-time jobs after they retire from their careers.', 'People seldom change their dietary and other health habits after retirement.', 'Unemployed retired people are even more likely to have heart attacks than are people who have jobs.']