A recent study has found that, surprisingly, the risk of serious injuries to workers is higher in industries that are monitored by government safety inspectors than in industries that are not so monitored. Which one of the following, if true, most helps to explain the surprising finding described above? ['Government safety inspectors do not have the authority to enforce safety regulations.', 'Workers behave especially cautiously when they believe their performance is being monitored by government safety inspectors.', 'Only those industries with an inherently high risk of on-the-job injury are monitored by government safety inspectors.', 'Government safety inspectors not only monitor but also train employees of the inspected firms to follow safe practices.']