he was not able to pass the exam.=he ---- ----passing the exam.

he was not able to pass the exam.=he ---- ----passing the exam.
he was not able to pass the exam.=he ---- ----passing the exam.

he was not able to pass the exam.=he ---- ----passing the exam.
He failed in passing the exam

不能，be able to do sth 没有 be able doing sth。这里后面是“passing the exam”。