Why is the ending of "Charles" ironic?

A.
The narrator and readers are surprised when they find out that Laurie is resposible for all of the bad things he said Charles did.

B.
The narrator and readers are concerend when they learn that Charles hurt other children in the class.

C.
The lighthearted tone of the story suddenly shifts as the narrator and readers are shocked by the truly terrible news given at the end of the story.

D.
The humor disappears as the narrator and readers learn that the kindergarten teacher is the mother of Charles.