A Study Was Conducted to Determine Whether a Videotape Would

A study was conducted to determine whether a videotape would be more effective than a pamphlet in instructing college-age women to perform breast self-examination on a regular basis.Which of the following conditions could be considered an antecedent variable?

A) Four participants in the pamphlet-based instruction group had mothers who had been diagnosed with breast cancer, and the other group had no participants with mothers diagnosed with breast cancer.
B) The group that received the videotape training comprised members of one sorority, and the group that received the pamphlet-based instruction comprised members of a different sorority.
C) During the study, most participants received flu shots through the college's student health service.
D) The pamphlet group had 38 members, and the videotape group had 33 members.