Why perfecto not Preterito indefinido here?

Question

The answer to ‘they were about to finish their exam’ is given as ‘Han estado a punto de...’

there’s no sense that this is the situation of ‘but something intervened’, and it doesn’t feel like a natural ‘perfecto’ tense to me, more just an action in the past. So I’m wondering why the perfecto was chosen here?

Answer

Hola KarenAll these sentences would be correct for "they were about to finish their exam":1. Ellos estaban a punto de terminar su examen.2. Ellos estuvieron a punto de terminar su examen.3. Ellos han estado a punto de terminar su examen.As what we're testing here is the structure "estar a punto de + infinitive", we are not adding any nuance to the sentences. We want the student to recognise "estar a punto de" as a way to say "to be about to do something". There is a note in the lesson though about a special nuance when using El Pretérito Perfecto with this structure which is to "nearly do" something but that something we understand didn't happen in the end. This sentence has that nuance. I hope this clarifies it.Un saludoInma

Answer

Just feedback.  For
me, although I appreciate that you are focusing on the use of estar a punto de
+ infinitive, I thought the answer would be more fitting using the imperfect
tense since there is no other information given.  I did read the note in the lesson, but in the
question, there is no note in parentheses stating that there was a conclusion.  I answered correctly by elimination, but I
found it confusing.