Ответ:

  1. Mrs. Harper screamed because her diamond necklace was gone.
  2. The six people were Mrs. Harper, her brother Tom, her friend Lucy, the waiter Paul, the gardener Ben, and the cook Anna.
  3. Detective Sam looked at the necklace box, the windows, and the door.
  4. Lucy was on the phone.
  5. Ben was outside watering the plants.
  6. He said, “I know who took the necklace.”