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.
If you want to stay longer than 180 days as a tourist, you have to apply for an extension at least 30 days before you're required to leave Canada. If your application wait time extends beyond your visa expiration, you'll be considered a temporary resident until a decision is made on the extension.rossing Into Canada. You'll need your U.S. passport to travel into Canada by air. Since the Western Hemisphere Travel Initiative went into effect in 2009, you can cross into Canada by land or water with any approved travel document.