The correct answer is “to force the audience to use
its imagination”.
Wilder wanted to challenge the audience to the see the play for what it was – a
play. He wasn’t a fan of the common convention of real-life theatre. It was
popular at the time to fill the stage with artifacts to make it seem like there
was a specific time and place in the play, carrying the audience on a journey.
Instead, Wilder rejected that aspect, he did not wish for the illusion of real
life, as he actively encouraged the audience to see the artifice.