单项选择题

A century ago, most families (47)______ on income from agriculture. Today, over half of all labor is in white-collar (48)______ . a (49)______ that includes doctors, lawyers, teachers, managers, and sales and clerical(文秘的) workers. Employment in blue collar work (assembly lines and construction are examples) and, especially farming, has declined over the years. The most (50)______ change in labor markets over the past few decades has been the surge (激增) of women into the labor (51)______ . In the 1950s, only one woman in three worked outside the home, more than half hold jobs today, and 44 percent of all workers are mothers with small children. Even more remarkable is the threefold increase in working mothers with small children. Several theories have been (52)______ to explain these changes. A revolution of rising (53)______ about living standards propelled many women into the workforce who might have been housewives in an earlier era. Legal reforms and changing attitudes about women’’s work roles have opened doors to careers that were previously closed. The flight from the worst types of household hard work was (54)______ by such innovations as washers and dryers, microwave oven. Options to postpone children and control family size have been made available by cheap and effective birth control, also increasing women’’s labor force (55)______ rates. These changes have not occurred in a (56)______ . The labor force participation rates of men fell slightly over this same period, partially because more young men are going to college, while mature men have typically been retiring at earlier ages. Word Bank A) facilitated I) grasped B) advanced J) expectations C) vacuum K) participation D) primarily L) journal E) relied M) category F) mixture N) force G) occupations O) literary H) dramatic