父母去年來過，住了半年，現在在國內，最近簽證要過期了。一定要過期之後才能重新申請嗎？
-Not really. If they will come to US after their current B2 visa expires, they can apply for the new B2 visa before the current B2 visa expires (no law limits that).
這次想去加拿大和墨西哥玩玩，可以在中國直接申請這些國家的簽證嗎？
-Yes.
如果來美國再申請呢？
-Up to them. But they do not need a visa to enter Mexico if they go to Mexico from US directly (the Mexico Customs officer will give the tourist visa to them at the entry point). But they need to get the Canadian visa to enter Canada.
