研究生考试一般都什么时候报名啊？

“抗大”的教学方法有哪些？

在我国，守法的主体包括（　　）。
A.一切国家机关
B.中华人民共和国全体公民、一切组织
C.在我国领域内的外国组织、外国人和无国籍人
D.社会组织

American farmers have been complaining of labor shortages for several years now.Given a multi-year decline in illegal immigration,and a similarly sustained pickup in the U.S.job market,the complaints are unlikely to stop without an overhaul of immigration rules for farm workers.Efforts to create a more straightforward agricultural-workers visa that would enable foreign workers to stay longer in the U.S.and change jobs within the industry have so far failed in Congress.If this doesn’t change,American businesses,communities and consumers will be the losers.Perhaps half of U.S.farm laborers are undocumented immigrants.As fewer such workers enter the U.S.,the characteristics of the agricultural workforce are changing.Today’s farm laborers,while still predominantly born in Mexico,are more likely to be settled,rather than migrating,and more likely to be married than single.They are also aging.At the start of this century,about one-third of crop workers were over the age of 35.Now,more than half are.And crop picking is hard on older bodies.One oft-debated cure for this labor shortage remains as implausible as it has been all along:Native U.S.workers won’t be returning to the farm.In a study published in 2013,economist Michael Clemens analyzed 15 years of data on North Carolina’s farm-labor market and concluded,“There is virtually no supply of native manual farm laborers”in the state.This was true even in the depths of a severe recession.Mechanization is not the answer either—not yet at least.Production of corn,cotton,rice,soybeans and wheat have been largely mechanized,but many high-value,labor-intensive crops,such as strawberries,need labor.Even dairy farms,where robots currently do only a small share of milking,have a long way to go before they are automated.As a result,farms have grown increasingly reliant on temporary guest workers using the H-2A visa to fill the gaps in the agricultural workforce.Starting around 2012,requests for the visas rose sharply;from 2011 to 2016 the number of visas issued more than doubled.The H-2A visa has no numerical cap,unlike the H-2B visa for nonagricultural work,which is limited to 66,000 annually.Even so,employers frequently complain that they aren’t allotted all the workers they need.The process is cumbersome,expensive and unreliable.One survey found that bureaucratic delays led H-2A workers to arrive on the job an average of 22 days late.And the shortage is compounded by federal immigration raids,which remove some workers and drive otherunderground.Petitioning each year for laborers—and hoping the government provides enough,and that they arrive on time—is no way to run a business.In a 2012 survey by the California Farm Bureau,71 percent of tree-fruit growers and nearly 80 percent of raisin and berry growers said they were short of labor.Some western growers have responded by movingoperations to Mexico.Without reliable access to a reliable workforce,more growers will be tempted to move south.According to a report by the Partnership for a New American Economy,Americans are consuming more fresh produce,which is good.But a rising share of it is grown elsewhere.In 1998-2000,14.5 percent of the fruit Americans consumed was imported.Little more than a decade later,the share of imported fruit had increased to 25.8 percent.Rural U.S.communities that might have benefited didn’t.In effect,the U.S.can import food or it can import the workers who pick it.The U.S.needs a simpler,streamlined,multi-year visa for agricultural workers,accompanied by measures to guard against exploitation and a viable path to U.S.residency for workers who meet the requirements.Otherwise growers will continue to struggle with shortages and uncertainty,and the country as a whole will lose out.
　　One trouble with US.Agriculture workforce is___《》（）

A.the rising number of illegal immigrants.
B.the high mobility of crop workers.
C.the lack of experienced labors.
D.the aging of immigrant farm workers.