English Grammar review

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Across
  1. 1. modal for possibility (5 letters)
  2. 4. past tense of "go" (4 letters)
Down
  1. 1. modal for obligation (4 letters)
  2. 2. present perfect auxiliary (4 letters)
  3. 3. present continuous auxiliary (2 letters)
  4. 4. future auxiliary (4 letters)