Pude terminar el examen antes de que sonara la campana

Question

Pude terminar el examen antes de que sonara/suene/haya sonado la campana.Hola! Podrías explicar por qué tendríamos que usar 'sonara' aquí en lugar de 
'suene' o 'haya sonado'? Serían todas correctas y simplemente 
significan cosas diferentes? Gracias!

Accepted Answer

Hola Tali
The reason why we need "antes de que sonara" is because in the main clause you have a past tense: pude..., so the logical sequence of tenses would be that. Sonara would place the action in the past:  I couldn't finish the exam before the bell rang. 
If we said "antes de que suene", using the present subjunctive, the action of "sonar" would be in the future and it wouldn't make sense as we would be saying: I couldn't finish the exam before the bell rings ??? 
The same goes for "haya sonado" as this will also convey an action in the future: I couldn't finish the exam before the bell has rang.??
To use either the present or the present perfect subjunctive you'd need a different tense in the main clause:
No podré terminar el examen antes de que la campana suene/haya sonado. 
I won't be able to finish the exam before the bell rings / has rang. 
I hope this clarified it.
Saludos