Snakes, Closed Spaces, Wild Animals, and Airplanes Are Common Sources

Snakes, closed spaces, wild animals, and airplanes are common sources of phobias for humans. Why might it be that humans are less often treated for phobias involving rainbows, smiles, or cheerful people?

A) Negative events do not happen to us with positive stimuli.
B) We are biologically and cognitively prepared to acquire certain fears.
C) Positive events do not happen to us with negative stimuli.
D) We are systematically exposed to more negative stimuli.