The correct answer is A) craft union.
The United Association of Plumbers and Pipefitters is a labor union that seeks to unite plumbers and pipefitters from around the country. The members of this union exhibit the same set of skills and are proficient in relatively similar tasks. Such an association is most likely an example of a craft union.
A craft union is the type of union that represents workers that have similar skills or work in the same tasks in different industries such as the case of this question, plumbers. This union is formed to improve the working conditions of the workers and demand better wages,