Some knowledge tests make a distinction between prohibitions and restrictions by law.
An absolute prohibition means that you are not allowed to do something under any circumstances.
When something is restricted by law it means that you may or may not do something, depending on the situation.
The use of a cellphone is a typical example of something that is restricted by law. Some states only allow the use of a cellphone with a handsfree device and only for drivers over a certain age. Others restrict the use of text messaging.
You are usually allowed to use a cell phone in an emergency.
In other words, no state completely prohibits the use of a cell phone while driving.
Smoking with a minor in the vehicle is an example of a prohibition. Where this is a law, there are no exceptions. Meaning, it is not allowed to smoke with a minor in the vehicle under any circumstances.
If you see both restricted by law and prohibited by law as alternatives on your knowledge test, think carefully before you answer.