Определить инфинитив и его форму в предложениях 1) to save him was impossible. 2) the first practical result in this branch of law is known to have been achieved even in the roman empire. 3) about 40 students were thrown into prison to be charged with various offences. 4) the barrister was glad to present this man at the trial.
2) to have been achieved - Perfect Passive
3) to be charged - Non-Perfect Passive
4) to present - Non-Perfect Active