My Extremely Hard Crossword

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Across
  1. 3. It is ________ to try and learn everything.
  2. 6. It is ________ how many planets there are in the universe.
  3. 7. ______ you like to try this crossword?
  4. 8. Nominalisation for helpless.
Down
  1. 1. No rest
  2. 2. The people who decide what happens to the constitution
  3. 4. Aliens are ______.
  4. 5. What trees are made of.
  5. 9. The element Arsenic is a _____.