Let p: it is cold, q: it is humid, and r: it is snowing. Which statement represents "It is cold and humid if and only if it is snowing”?

“Cold and humid” is represented by p ∧ q, while “snowing” is r. A statement “X if and only if Y” means both X → Y and Y → X, so the sentence becomes [(p ∧ q) → r] ∧ [r → (p ∧ q)]. This is choice C. Choice D is equivalent, since it separately states that p and q each follow from r and each imply r, but C directly expresses the two directions between p ∧ q and r.

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