check即行政审理administrative processing。看到很多朋友在申请签证时都遇到了被check的问题，但是又不知道到底check是什么，所以我这里整理了一些check的资料，尽量全面解释check的含义，我在这篇文章中说到的check问题，主要是针对美国留学签证F1签证，如果大家能够补充F2，B类，和J1等等签证的check经验，以及我帖子中写的不合适的，不足的地方，在此感激不尽，最后祝愿所有的checkees都能顺利早日clear。
注：check就是官方说的行政审理即administrative processing
check的定义和check的目的
check这个词是广大签友们取的名字，在美国使馆的官方说法是行政审理，即就是administrative processing，主要是指对一些签证申请者的材料，进行更近一步的审查，其所花费的时间比一次性通过签证审查的人所需要的时间要多。主要审查的目的，根据美国国防院的说法，主要有四点：
1、从根本上防止大杀伤性武器和导弹技术的扩散；
2、限制在世界一些地区发展影响区域安全的传统武器；
3、防止向恐怖主义国家输送军火和军民两用物品；
4、确保美国在某些军事科技上的优势
以下为节选自原文，仅作参考：
Media Note
Office of the Spokesman
Washington, DC
February 11, 2005
Extension of Validity for Science Related Interagency Visa Clearance
Visa applications for persons to study or work in certain sensitive scientific and technical fields are subject to an interagency clearance in Washington, DC, called Visas Mantis. Since 1998, the Visas Mantis clearance process has been used to screen against the illegal transfer of technology. Once the clearance process is complete and a visa is issued, the individual may apply for admission at a U.S. port of entry. Visas Mantis clearance and visa validity are different than the period of admission determined by a Department of Homeland Security officer at the port of entry. The U.S. Department of State, in consultation with the U.S. Department of Homeland Security, has extended the validity of Visas Mantis clearances for the F (student), J (exchange visitors), H (temporary workers), L (intracompany transferees) and B (tourist and business) categories of visas. This means that if the original visa has expired and a new visa application is filed to return to the previous study or work program in the United States, another Visas Mantis clearance may not be required. Consular officers have the discretion, if warranted, to request a Visas Mantis clearance during any visa adjudication. International students (F visas) who have received a Visas Mantis clearance and been issued a visa will benefit from having that clearance be valid for up to the length of the approved academic program, to a maximum of four years. If a student changes academic programs, the clearance will no longer be valid and a Visas Mantis review would be required should the applicant reapply for a new visa.
