Identify the relative clauses in these sentences. (Some contain more than one.) Rewrite them as participle or infinitive clauses.
1 The word astronaut, which is formed from two Greek words, means 'star sailor'.
2 Only flights which reach an altitude of 100 km or more are considered space flights.
3 NASA astronauts are given a difficult training programme which they have to complete after twenty months.
4 Astronauts who spend long periods in space do exercises which have been designed to keep them strong.
5 Spacecraft which intend to escape from Earth's gravity need to reach a speed of about 40,000 km/h.
6 The film Apollo 13, which was made in 1995, is a very interesting film on space travel that should be seen.