The given sentences relate to unions and legislation about unions. Select the option that best completes each sentence.

Unions can take a variety of forms. Companies can be required to hire workers who belong to a particular union prior to employment in what is called $a(n)$

A is a situation where firms can hire nonunion individuals, but those nonunion workers are required to join the union soon after being hired.

When employees can either join the union or not, but must still pay union dues, this is known as

Alternatively, states can pass laws that prohibit union shops by what are known as laws.