A Study Compared Weight Loss in Obese Subjects Between Those

A study compared weight loss in obese subjects between those who participated in a support group and those who chose not to.Which of the following factors or conditions in the study would be considered an intervening variable?

A) Data collection for both groups occurred over the Thanksgiving holiday.
B) The group that did not participate in a support group had a greater percentage of male subjects.
C) Three subjects were diagnosed with hypertension 1 month after the study began.
D) Two subjects dropped out of the study 1 month after the study began.