Little Jack Horner

Little Jack Horner
Sat in a corner,
Eating his Christmas pie.
He put in his thumb,
And he pulled out a plum,
And said, "What a good boy am I!"

Why did Jack think he was a good boy?

A. Because he had a Christmas pie.
B. Because he sat in a corner.
C. Because he put his thumb in the pie.
D. Because he found a plum in the pie.