The high-tech zone of a city is far from the old city and there are few buses. Most of the employees of high-tech companies live in the old city, and they often arrive late because they can't get on the bus on time. For this reason, the number of bus companies has increased significantly. In order to meet the travel needs of these employees, the bus frequency between the high-tech zone and the old city was met, but after a period of observation, the situation has not improved, and these employees are often late. Which of the following is true to best explain the above phenomenon? ['Many enterprises in high-tech zones have adjusted their working hours.', 'Some employees of high-tech zones that used to drive to work switched to buses.', 'Due to narrow roads, long traffic jams often occur after a large increase in bus frequency.', 'Many high-tech zone employees who used to take buses to work instead of drive or take taxis.']