完形填空 　At the start of the 20th century, immigrant labor and innovation helped turn the U. S. into a powerful manufacturing nation. Today, foreign-born engineers jam the corridors of Silicon Valley,helping America''s information-technology boom. And as the 21st century dawns, yet another wave of immigrants will once again help transform the economy. 　　46)During the next decade, excepting a change in government policy, nearly a million immigrants are expected to arrive in the U. S. every year,most of whom,both legal and illegal,will continue to come from Latin America and Southeast Asia, but every foreign land will be represented. 　　As domestic birthrates stagnate, only foreign-born worker will keep the labor pool growing. By 2006, in fact, immigrants will account for half of all new U. S. workers; over the next 30 years, their share will rise to 60%. 　　47) Even at current levels of immigration, according to the Labor Dept. the number of people available to work will increase by a mere 0.8% per year between 1996 and 2006-half the rate of the previous decade. Without immigrants, according to a new study, the U. S. workforce would actually begin to shrink by 2015. 　　48) It''s not all about sheer numbers, of course:To lift productivity and spur growth, immigrants must provide creativity, entrepreneurial energy, or simple initiative that America couldn''t find otherwise. "If all you did was bring in people who are exactly the same as those we have here, there would be no economic benefit," says Rand Corp. economist James P. Smith, "You''d just have more people." 　　Just as crucial, the array of education and skills immigrants bring could fit neatly with the supply of jobs over the next decade. According to Linda Levine at the Congressional Research Service,60% of the jobs created through 2005 will require some post-secondary education. But, she adds, low-skill jobs will still represent about half of total employment. 49) Yet immigrants also are 50% more likely than Americans to have a graduate degree, and an unbelievable 23% of U. S. residents holding PhDs in science and engineering are foreign-born, according to the National Science Foundation. 　　Indeed, foreign-born workers have shown an extraordinary ability to assimilate and flourish. Certainly, some less skilled workers will remain at the bottom economic rung all their lives. 50) Yet others will catch up quickly, and within a decade of their arrival, the well-educated will go from making barely half that of native-born Americans in comparable work to nearly 90%, according to a recent study. 　　That, of course, will raise immigrants'' living standards. More important, it will help drive innovation and entrepreneurship,key engines of the 21st Century Economy.