In determining the speed of a vehicle at a collision scene, the officer must be able to determine the drag factor of the roadway. Which of the following is true?

a. the drag factor is a constant number for all roadways
b. the drag factor will vary on each road surface
c. the drag factor will change on a road surface when the surface is wet
d. both b and c are true: a is false
e. both a and c are true: b is false