From this passage, the reader can safely infer that a) the porter is an old man. b) the porter murdered the king. c) the porter is a comic character. d) the porter is an enemy of macduff.

From the passage, the reader can safely infer that the porter is a comic character.

Explanation:

In this story, the porter plays for comic relief by reducing the tension of the audience on the murder of the king Duncan.The porter also indicates the gates to Macbeth's home. The porter was a drunken character and he has a lively imagination.This porter character will speak humorously about his superiors. He only led Macduff into the Macbeth castle.

To get what you want you have to work for it.

Bis correct you are right