FYI. It's now added as a hint. "Libre" is also a default translation. "Disponible" (available) is not a word taught in the French course, but "available" appears in the reverse course. Hence its appearance in this reverse exercise.
If DL means 'available' then disponible is clearly correct - but to use 'free' and translate as disponible presumes a context not given. A prisoner could be speaking for instance. If there is no context either is acceptable in UK English