A research institution took 9 years to track and investigate the dietary habits of 60,000 healthy people, including two types of digestion of meat, meat cooking methods, and meat cooking degree. The research team took the research object according to the amount of meat consumed. Divided into 5 groups. By the end of the study, a total of 208 people had pancreatic cancer, most of them were concentrated in the two groups with the highest amount of barbecued meat. Therefore, the researchers concluded that eating a large amount of barbecued meat is more likely to develop pancreatic cancer. Which of the following is true will most weaken the conclusion. ["Studies show that if one parent has pancreatic cancer, their child's chance of developing pancreatic cancer will increase by 30%.", 'Research shows that compared with people who eat cooked meat for a long time, people who eat meat for a long time have a similar proportion of pancreatic cancer.', 'Survey data shows that 98% of people who eat a lot of barbecues like to eat barbecue while drinking beer, and often stay up late.', 'The proportion of people who prefer semi-cooked barbecue in this study to pancreatic cancer is about 60% higher than those who prefer fully-cooked barbecue.']