The answer is B because that is the biggest thing that happened to Nicolo
I believe C) to narrate her experiences as a mental patient.
Similes compare two things. Because clowns are considered by most to be very funny, the object would also have to be something funny.
Therefore you could say...
A clown is as funny as a medieval joker.
A clown is as funny as a cat barking like a dog.
A clown is as funny as a comedy movie.