Bicycle Riders Modals 2, Necessity / Lack of Necessity

A Verb Quiz
From the English Zone

Modals 2 - Necessity / Lack of Necessity
Choose the correct modal (helping verb) to complete the sentence.

Bicycle riders have a driver's license to ride. It's not necessary.
People who ride motorcycles have a driver's license. It is the law.
Drivers on the freeway be very careful because speed kills!
People who ride horses take their horses on the freeway! That would be a stupid thing to do!