The compound propositions (p → q) → r and p → (q → r) are not logically equivalent because _____.
A. when p, q, and r are all false, (p → q) → r is false, but p → (q → r) is true
B. when p, q, and r are all false, both (p → q) → r and p → (q → r) are true
C. when p, q, and r are all true, (p → q) → r is false, but p → (q → r) is true
D. when p, q, and r are all false, both (p → q) → r and p → (q → r) are false