Thirty students from Jinghua University recently agreed to participate in a program aimed at improving dating skills. One month before joining the program, they had had an average date.30 students were divided into two groups: the first group and 6 Different volunteers made 6 "internship" appointments, and received feedback from their dated views on their appearance and behavior; the second group was only the control group. Each group must be filled in separately before the internship date Social anxiety questionnaire, and scores on their social skills. After internship dating, the first group needs to fill out the questionnaire again. The results show that the first group shows less social anxiety than the control group and is more socially friendly Confidence and easier dating. Obviously, actually dating can improve our social communication. Which of the following, if true, is most likely to challenge the above inference? ['Experts have different views on whether such training programs can be implemented universally.', 'The students participating in this training program are not randomly selected, but all students who signed up do not know what the experimental program will include.', 'The control group complained afterwards that they did not know that the plan had begun. Therefore, the questionnaire they filled out was more worried because they had expectations for the future.', 'When filling out the social anxiety questionnaire, students need to remember certain dating situations. Male students generally have more objective evaluations of dating targets, while female students appear more emotional.']