It is a warning that indicates a future event.
<span>"two different writers have made Rosencrantz and Guildenstern into main characters"
The other three options might be true, but they are not directly stated in the passage. The only clear statement that the author makes is that two different authors (Stoppard in "Rosencrantz and Guildenstern are Dead" and Gilbert in "Rosencrantz and Guildenstern") took those two characters and make them the focus of their play.</span>
