David P Abbot was a US magician who ____ (invent, invented, has invented) the basis of ball trick in 1907. He ______(use, had, used) to make a golden ball float around his parlour. Abbot ____ (could, would may) absent-mindedly leave the ball on a book shelf. Guests would sneak over the left ball and _____(find, found, have found) it was much heavier than a thread could support.