Choose the correct word

1. When the boat started sinking, the captain sent out a distress
   [signal|shred]
   .
2. Scientists believe the
   [cosmos|civilisation]
   is about 15 billion years old.
3. Please close the curtains. There's a
   [channel|beam]
   of light coming in from the window.
4. I'm thinking of having
   [light|laser]
   surgery to correct my eyesight.
5. Earth completes its
   [orbit|wave]
   around the sun in 365.26 days.
6. Astronomers use
   [telescopes|screensavers]
   to explore the universe.