Which word could correctly replace the word stern as it is used in this excerpt from Mark Twain’s The Prince and the Pauper?

Presently Tom found himself in a noble apartment of the palace and heard the door close behind him. Around him stood those who had come with him. Before him, at a little distance, reclined a very large and very fat man, with a wide, pulpy face, and a stern expression.

A.
irritated
B.
upset
C.
serious
D.
strict
E.
angry