1)i just (to learn) that he (to be going) to make a report at the conference. 2) they were very tired after their journey: it (to take) twelve hours. 3) the students are busy now: (to do) their laboratory work. 4) i (to think) your words over.

1) I have just learnt that he (is going) to make a report at the conference.
2) They were very tired after their journey: it (had taken) twelve hours.
3) The students are busy now: (are doing) their laboratory work.
4) I (will think) your words over.