Bill Drives Faster Than the Speed Limit Only When His

Multiple Choice

Bill drives faster than the speed limit only when his friends are in the car with him because they tell him he is cool.He doesn't speed when his parents or girlfriend are in the car because they don't say it's cool.What is the S^D in this example?​

A) ​parents
B) ​girlfriend
C) ​friends
D) ​parents and girlfriend