The correct option is
C It provides necessary information.
Option C: In order to completely understand a character or a story, some form of background information on the important characters is essential. Without an exposition, the reader would not have a clear understanding or context of the plot. Hence option C is most suitable: exposition provides the necessary information to a story.
Option A: This is not the reason behind an exposition. It does make the reader learn new things about character and plot, but for the sake of the story. Hence it isn't the main purpose.
Option B: Similarly, exposition does not necessarily increase the reader's interest. It isn't the main reason.
Option D: Background information describes the past, so that the reader can understand the present better. Foreseeing the future is a far shot.
Hence options A, B and D are wrong.