Identify the Variable of Interest in the Study

Identify the variable of interest in the study.
-The highway department paves one section of an Interstate with Type A concrete and an adjoining section with
Type B concrete and observes how long it takes until cracks appear in each.

A) The difference between the measured length of time it takes for cracks to appear in each type of concrete
B) Whether Type A concrete provides better traction than Type B concrete
C) The difference between cost of the two types of concrete