Read the excerpt from Romeo and Juliet. Romeo: "Peace, peace, Mercutio, peace! - Thou talk'st of nothing." Mercutio: "True, I talk of dreams, - Which are the children of an idle brain, - Begot of nothing but vain fantasy, - Which is as thin of substance as the air - And more inconstant than the wind". What kind of dreams is Mercutio describing, especially when he calls them "Children of an idle brain"?
A: Childish, immature thoughts
B: The strange thoughts that come when our minds are at rest
C: The dreams and hopes of our youth that have long since blown away
D: The nightmares that come from an overactive imagination