excerpt from Act III, Scene III of Shakespeare's Hamlet

Polonius. [Speaking to King Claudius]
My lord, he's (Hamlet's) going to his mother's (Gertrude's) closet.
Behind the arras I'll convey myself
To hear the process. I'll warrant she'll tax him home;
And, as you said, and wisely was it said, 2310
'Tis meet that some more audience than a mother,
Since nature makes them partial, should o'erhear
The speech, of vantage. Fare you well, my liege.
I'll call upon you ere you go to bed
And tell you what I know.

Why does Polonius say that he will spy on Hamlet's conversation with his mother?
A) Polonius believes that Gertrude is plotting with Ophelia against Hamlet.
B) Polonius claims that Gertrude will be too partial and forgiving to her own son.
C) Polonius wants to find out why the Queen is so attracted to Claudius.
D) He wants to play a practical joke on Hamlet.

Hamlet, one of the best-known works of William Shakespeare, tells the story of Hamlet, Prince of Denmark, who has to face the murder of his father, the king, by the hand of his own uncle, and is inmersed in a constant state of vengeful ploting and self-analysis that comes from his being demanded by the ghost of his own father to wreak revenge on his murderous uncle. In Act 3, Scene 3, most specifically, King Claudius is plotting a way to get rid of Hamlet and convinces his vassals and even the friends of Hamlet, that he has gone crazy and needs to be sent away to England. After talking to the two men, Rosencrantz and Guildenstern, who will gladly help the King get rid of Hamlet, King Claudius is approached by Polonius who, like the others, wishes only to please the King and offers himself to spy on Hamlet´s upcoming conversation with his mother, Gertrude. The reason why Polonius offers such a thing is that he tells the King that mothers cannot be trusted when judging the words and thoughts of their children and will often be swayed in favor of them. This is why the correct answer is B.