Which of the Following Is Least Likely an Appropriate Bargaining

Which of the following is least likely an appropriate bargaining unit?

A) all teachers in a particular state
B) all workers at a particular plant of a company that has four other similar plants
C) all the maintenance workers at a single plant
D) the production workers at one plant and the maintenance workers at another company's plant
E) all the production workers at a company's six plants located in six states