ABC Blocks magic trick

This is a classic magic trick. The magician presents three blocks (or cubes) marked with the letters A, B, and C. First, the magician might show an empty bag or hat and then place the blocks inside, or simply introduce them into it. Next, the magician takes the blocks out one by one (or stacks them directly if the bag wasn't used initially) onto a stand or base that has a central rod or post. Once stacked, this tower of blocks is covered with a hollow tube or box, which the magician has previously shown to the audience to demonstrate it's empty. After a moment, upon lifting the cover, one of the blocks has magically vanished from the stack. To the audience's great astonishment, the vanished block reappears inside the bag or hat that was shown at the beginning!