Translation:I do not know what they have had to drink.
In many questions duolingo injects "could", somewhat on it's own whim, yet in other questions such as this one there is no sign of the subjunctive in the English translation. Abbiano is subjunctive, implying uncertainty and in order to imply that same concept in English you need may/might/could
Agreed. I've gotten through the lessons more easily by thinking through the translation in Spanish, which seems to match Italian's use of the subjunctive almost perfectly. Then I just tell Duolingo what it wants to hear... which, IMHO, is still wrong. But I'll go with the flow. :-)
"bere" = the infinitive => to drink
"beve" = conjugated form of "bere" for 3rd person singular present indicative. => "he drinks", "she drinks", or "it drinks".
Voglio qualcosa da bere. I want something to drink.
È sempre così quando beve troppo. It's always like this when he drinks too much.