Gas exchange is the delivery of oxygen from the lungs to the bloodstream, and the elimination of carbon dioxide from the bloodstream to the lungs. It occurs in the lungs between the alveoli and a network of tiny blood vessels called capillaries, which are located in the walls of the alveoli.
Admitted for 180 days â Canadians admitted in âVisitor for Pleasureâ or B-2 status without a B-2 visa in hand are deemed to be admitted for 180 days under current US Customs and Border Protection (CBP) interpretation of the rules.
Residents of Canada are allowed to stay in the U.S. for up to six months in any consecutive 12-month period on their virtual B2 visa. Explanation: The B2 visa is the immigration category covering leisure visits, tourism, and non-business travel. It is not a specific piece of paper.