Strayer and Colleagues Wanted to Establish If There Was a Causal

Strayer and colleagues wanted to establish if there was a causal relationship between cell phone use while driving and increased risk of vehicular collision. The independent and dependent variables in that experiment were, respectively:

A) the undergraduate students with a range of driving experience and visual acuity, and whether or not the person was talking on a cell phone.
B) the braking reaction time and whether or not the person was talking on a cell phone.
C) whether or not the person was talking on a cell phone, and the braking reaction time.
D) whether or not the person was talking on a cell phone, and the undergraduate students with a range of driving experience and visual acuity.