Complete the sentences with the given collocations

• carbon dioxide
• final frontier
• solar system
• space exploration
• science fiction
• nuclear war

1. The Earth's atmosphere contains[ ]gas.
2. Space is often referred to as the[ ]; the unexplored territory.
3. The[ ] is made up of all the planets that orbit the sun.
4. Every new step we make in[ ] advances our knowledge of the universe.
5. The[ ] film is set on Mars.
6. The threat of[ ] is frightening.