Sam's parents took her to the World Park last week. He saw Big Ben, the Tower Bridge, Disneyland in America, the CN Tower, Niagara Falls and the Sydney Opera House. His father told her Big Ben and the Tower Bridge are in London. Her mother told her Niagara Falls is in Canada and the Sydney Opera House is in Australia. He learnt about many things of the famous places around the world.

在如图所示的电路中，闭合电键S，当滑动变阻器的滑动触头P向下滑动时，四个理想电表的示数都发生变化，电表的示数分别用I、U₁、U₂和U₃表示，电表示数变化量的大小分别用△I、△U₁、△U₂和△U₃表示．下列比值正确的是（  ）

下列器官中，空气和食物的共同通道是（    ）