"They have a terrible marriage."
Translation:De har et forferdelig ekteskap.
'dårlig' is accepted, but it would be better to use 'forferdelig' as this better translates 'terrible'. 'dårlig' is closer to 'bad/poor' or 'badly/poorly'.
Huh. I put "dårlig" and it was marked wrong. Perhaps it was the wrong inflection? Anyway, thanks for the explanation.