Tides and moon phases

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Across
  1. 5. it's an zone that has high and low
  2. 6. A zone that is very low
  3. 7. It's really high or low
Down
  1. 1. something that pulls things together
  2. 2. when it's high or low
  3. 3. a zone where it is very high
  4. 4. there is not much of a diff. between the high and low