up
自己查了一下
墨西哥的美国大使馆说第一次签证的不可以在墨西哥签,如下
Who Cannot Apply in Mexico:
Applicants who entered the U.S. with a visa issued in their home
country and changed status with Department of Homeland Security in the U.S.
who seek a new visa in the new visa category. .
Applicants who entered the United States in one visa category and are
seeking to re-enter the U.S. in a different visa category.
加拿大的美国使馆说
consular officers in Canada will likely refuse to issue a visa to first-time
student or work visa applicants if their education and/or work experience
is solely or predominantly from a country other than the United States or
Canada. Note also that there are some risks associated with applying for a
visa in Canada. If the consular officer does not approve the visa, the
applicant may not be able to return to the United States. Even successful
applicants may be required to stay for an extended period until a decision
has been rendered. Please consider all these expenses and time delays before
scheduling an appointment.