A school newspaper was commissioned by the Student Union to conduct a sample survey among the teachers and students of the school and select the most popular student union cadres. As a result, Yao Jun received more than 65% of support and received the most votes. Based on this, the Student Union considered that the most popular student union cadre was Yao Jun. Which of the following, if true, would weaken the student union's conclusions most. ['Most of this survey came from the department where Yao Jun is.', 'Most respondents do not pay attention to student union members and their work.', 'Some of the teachers and students of the school did not express their opinions in the survey.', 'The design of this questionnaire puts Yao Jun first.']