I tried 'they raise the bridge', thinking of a drawbridge or something like Tower Bridge in London, but it wasn't accepted. I've reported this, but perhaps in Irish such a bridge is opened or something, rather than raised. Does anyone know? A drawbridge is apparently 'droichead tógála' (http://breis.focloir.ie/en/fgb/droichead).
It looks like ardaigh (“raise”, “draw”) is the preferred verb, though I don’t know whether that refers only to the strict definition of a drawbridge (i.e. the type used with castles for crossing their moats) or to movable bridges in general (e.g. bascule bridges such as Tower Bridge).
Tógann said does mean "they take", and if the sentence was Tógann said an t-úll, then "They take the apple" would be the most sensible translation. But the course contributors want you to understand that if you want to say "They build the bridge", then the Irish is Tógann siad an droichead.
The sense of "They take the bridge" meaning "they go by way of the bridge" is probably béarlachas, but you will hear Tógann siad an droichead used in that way. Just be aware that that isn't always what tógann means, and, in the case of something like a bridge, the "build/construct" meaning has to be considered.
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