Past Perfect Tense modal verbs:
Die Modalverben werden hier in allen Personenformen gleich gebildet.
can – had been able to
can’t – hadn’t able to/had been unable to
need not – hadn’t had to
may – had been allowed to
must – had had to
must not – hadn’t been allowed to
need not – hadn’t had to
shall – had been to
Past Perfect or Past Simple
a) After they had had to study a lot, they could/were able to pass the exam.
b) After she had been allowed to buy a horse, she had to clean and feed it.
c) He hadn’t been able to finish his work until the time elapsed.
d) After Jane hadn’t been allowed to go the cinema, she was able to meet her girlfriend.
e) As I hadn’t had to learn more, I was able to go for walk.