Research suggests that high school students could benefit from later school starting times. A school administrative team is considering a proposal to move the starting time of the local high school one hour later than the current start time. To measure interest in the proposal, members of the team randomly select subjects attending a large soccer tournament played on the high school grounds on a Saturday morning. The team finds that 58% of those surveyed support a later high school start time. Which type of bias is most likely to be present in the survey results? a. This is undercoverage bias because adults with children are more likely to be included in the sample.
b. This is question wording bias because the phrasing of the later start times question may be confusing to some subjects.
c. This is nonresponse bias because some of those selected may choose to not provide their opinion on later start times.
d. This is voluntary response bias because vocal supporters of later start times will be more likely to offer their opinion.

I was thinking d. Who else thinks this is right too?