One picture holds all three uses: two sides on opposite sides of a border, each handing over what is theirs and taking back the other side's version of the same thing. Usually what crosses is money — my dollars for your euros — and the words then cover both the trading and the money that comes in from it. Once, what crosses is people: my school year in your country, yours in mine. The little word a is what tells you which crossing is meant, because the money uses take no article and the student one does.
三個用法可以用同一個畫面裝起來：兩邊各在國界的一側，各自把自己的東西交出去，換回對方那一份。多數時候過境的是錢——我的美元換你的歐元——這組字於是同時蓋住「換錢這件事」和「換進來的錢」。有一個用法過境的不是錢，是人：我去你的國家念一學期，你來我的國家念一學期。要分辨指的是哪一種，看前面有沒有 a：錢的兩個意思不可數，學生交換那個意思可數。
登入就可以看每一支怎麼連回核心畫面。