In the investigation of the cause of a certain production accident, 70% of people believed that it was a malfunction of the equipment: 50% thought it was an illegal operation: 25% thought that the reason was unclear and needed further investigation. Which of the following best explains the seemingly contradictory statement above? ['25 people surveyed.', 'Have their own opinions changed.', 'Some investigators believe that the accident has both the cause of equipment failure and the cause of illegal operations.', 'Many people with unexplained reasons actually have their own biased judgments, but are unwilling to disclose.']