单选题 .  At the heart of the debate over illegal immigration lies one key question: are immigrants good or bad for the economy? The American public overwhelmingly thinks they're bad. Yet the consensus among most economists is that immigration, both legal and illegal, provides a small net boost to the economy. Immigrants provide cheap labor, lower the prices of everything from farm produce to new homes, and leave consumers with a little more money in their pockets. So why is there such a discrepancy between the perception of immigrants' impact on the economy and the reality?
    There are a number of familiar theories. Some argue that people are anxious and feel threatened by an inflow of new workers. Others highlight the strain that undocumented immigrants place on public services, like schools, hospitals, and jails. Still others emphasize the role of race, arguing that foreigners add to the nation's fears and insecurities. There's some truth to all these explanations, but they aren't quite sufficient.
    To get a better understanding of what's going on, consider the way immigration's impact is felt. Though its overall effect may be positive, its costs and benefits are distributed unevenly. David Card, an economist at UC Berkeley, notes that the ones who profit most directly from immigrants' low-cost labor are businesses and employers—meatpacking plants in Nebraska, for instance, or agricultural businesses in California. Granted, these producers' savings probably translate into lower prices at the grocery store, but how many consumers make that mental connection at the checkout counter? As for the drawbacks of illegal immigration, these, too, are concentrated. Native low-skilled workers suffer most from the competition of foreign labor. According to a study by George Borjas, a Harvard economist, immigration reduced the wages of American high-school dropouts by 9% between 1980-2000.
    Among high-skilled, better-educated employees, however, opposition was strongest in states with both high numbers of immigrants and relatively generous social services. What worried them most, in other words, was the fiscal (财政的) burden of immigration. That conclusion was reinforced by another finding: that their opposition appeared to soften when that fiscal burden decreased, as occurred with welfare reform in the 1990s, which curbed immigrants' access to certain benefits.
    The irony is that for all the overexcited debate, the net effect of immigration is minimal. Even for those most acutely affected—say, low-skilled workers, or California residents—the impact isn't all that dramatic. "The unpleasant voices have tended to dominate our perceptions, " says Daniel Tichenor, a political science professor at the University of Oregon. "But when all those factors are put together and the economists calculate the numbers, it ends up being a net positive, but a small one." Too bad most people don't, realize it.1.  What can we learn from the first paragraph? ______