Final answer:
Hamlet is mocking Polonius by fabricating absurd images in the clouds, which demonstrates Polonius's gullibility as he believes Hamlet's nonsensical comments.
Step-by-step explanation:
In the iconic play Hamlet by William Shakespeare, the protagonist's interaction with Polonius while supposedly observing shapes in the clouds at the end of Act III, Scene II serves as a critical instance of character exposition. Hamlet is not daydreaming nor seeking hidden messages but rather, he is mocking Polonius by inventing absurd images (option b). This behaviour illustrates Hamlet's astute awareness of Polonius's nature and suggests that Hamlet is toying with him. In turn, this interaction reveals that Polonius is susceptible to deception, displaying his gullibility as he takes Hamlet’s nonsensical remarks seriously (option d).