回复：由加拿大返美差点被拒入境 - 应该放你进

根据国务院的这份文件: 过期的F-1签证可以在加墨入境时自动延期和更换类型. 你用的30天条款是I-94背后的把? 你应该打印这个文件就好了.

http://travel.state.gov/visa/laws/telegrams/telegrams_1441.html

---------摘要-------
(i) The validity of an expired nonimmigrant visa issued under INA 101(a)(15) may be considered to be automatically extended to the date of application for readmission, and

(ii) In cases where the original nonimmigrant classification of an alien has been changed by BCIS to another nonimmigrant classification, the validity of an expired or unexpired nonimmigrant visa may be considered to be automatically extended to the date of application for readmission, and the visa may be converted as necessary to that changed classification.