Answer:
He uses as an example a film that starts with a scene where two people strangle another person. The murderers have had their identity revealed since the beginning of the film. People know who was responsible for the death by strangulation throughout the film.
Step-by-step explanation:
Hitchcock says that the right way to make suspense is to let the audience play at being god, that is, the audience is omniscient in relation to history and knows everything from the beginning, unlike the characters in the film. The suspense is due to how this mystery (which the public already knows what it is) will be developed and solved by the characters within the plot and how it will move the story. In other words, Hitchcock claims that giving the public the power of knowledge creates the quality suspense.