Which of the Following Is the Best Example of an Injunctive

Which of the following is the best example of an injunctive norm?

A) Drivers are prohibited from parking within 10 feet of fire hydrants.
B) Drivers are encouraged to be courteous and help other drivers merge into traffic.
C) The city has posted a sign in front of the hospital entrance telling drivers of waiting cars to turn off their engines.
D) Drivers who are coming up in traffic behind a police car will not pass the police car very often.