I would like to know the answer to this question.

At a high school, the cafeteria staff provides optional comment cards to students eating in the cafeteria. Students who wish to make a comment can obtain and fill out a comment card and return it to a drop box in the front office. At the end of the semester, the staff analyzes the responses and finds that 72% of the students who filled out a comment card recommend major changes to the food selection. What conclusions can the cafeteria staff draw from these responses?

• (A) Since all of the students had an opportunity to respond, this is evidence that a majority of all the students supports major changes.
• (B) The cafeteria staff should not use the results to draw any conclusions since some students may not have filled out a comment card, which is nonresponse.
• (C) If the students recorded their grade level with their response, the staff could make the original sample a stratified sample and use the responses to learn what proportion of each grade recommends major changes to food selection.
• (D) The responses were from a voluntary response sample, so the cafeteria staff should not use the results to draw any conclusions.
• (E) The opportunity to fill out comment cards should be offered to students at all high schools in the school district to get a larger sample size, which will make the results more reliable.