From the 1900’s through the 1950’s waitresses in the United States developed a form of unionism based on the unions’ defining the skills that their occupation included and enforcing standards for the performance of those skills. This “occupational unionism” differed substantially from the “worksite unionism” prevalent among factory workers. Rather than unionizing the workforces of particular employers, waitress locals ((美)工会地方分会) sought to control their occupation throughout a city. Occupational unionism operated through union hiring halls, which provided free placement (工作安排) services to employers who agreed to hire their personnel only through the union. Hiring halls offered union waitresses collective employment security, not individual job security—a basic protection offered by worksite unions. That is, when a waitress lost her job, the local did not intervene with her employer but placed her elsewhere; and when jobs were scarce, the work hours available were distributed fairly among all members rather than being assigned according to seniority.
17. The primary purpose of the passage is to
(A) analyze a current trend in relation to the past
(B) discuss a particular solution to a longstanding problem
(C) analyze changes in the way that certain standards have been enforced
(D) apply a generalization to an unusual situation（E）
(E) describe an approach by contrasting it with another approach
18. Which of the following statements best summarizes a distinction mentioned in the passage between waitress unions and factory workers’ unions?
(A) Waitress unions were more successful than factory workers’ unions in that they were able to unionize whole cities.
(B) Waitress unions had an impact on only certain local areas, whereas the impact of factory workers’ unions was national.
(C) Waitress union members held primarily part-time positions, whereas factory workers’ unions placed their members in full-time jobs.
(D) Waitress unions emphasized the occupation of workers, whereas factory workers’ unions emphasized the worksite at which workers were employed.（D）
(E) Waitress unions defined the skills of their trade, whereas the skills of factory trades were determined by employers’ groups.
19. According to the passage, which of the following was characteristic of the form of union that United States waitresses developed in the first half of the twentieth century?
(A) The union represented a wide variety of restaurant and hotel service occupations.
(B) The union defined the skills required of waitresses and disciplined its members to meet certain standards.
(C) The union billed employers for its members’ work and distributed the earnings among all members.
(D) The union negotiated the enforcement of occupational standards with each employer whose workforce joined the union.（B）
(E) The union ensured that a worker could not be laid off arbitrarily by an employer.
20. The author of the passage mentions “particular employers” (line 8) primarily in order to
(A) suggest that occupational unions found some employers difficult to satisfy
(B) indicate that the occupational unions served some employers but not others
(C) emphasize the unique focus of occupational unionism
(D) accentuate the hostility of some employers toward occupational unionism（C）
(E) point out a weakness of worksite unionism