Which sentence below shows correct use of em dashes? (4 points)
by the end-of-the-story, no one could believe it the main-character, was dead.
by - the end of the story no one could believe it, the main - character was dead.
by the end of the story, no-one could believe it the main, character - was dead.
by the end of the story-no one could believe it-the main character was dead.

By the end of the story---no one could believe it---the main character was dead.

The above choice shows the correct use of em dashes.

em dashes are used to replace the commas, parentheses, and colons in a sentence. 
It is limited to two appearances to avoid confusion. 

The above choice used the em dash in replacement of the commas.
By the end of the story, no on could believe it, the main character was dead.