First Principles Thinking: PVBP Formula
A is correct. The CFA Curriculum defines PVBP as $\dfrac{PV_{-} - PV_{+}}{2}$, where $PV_{-}$ and $PV_{+}$ are bond prices at yields 1 bp lower and higher, respectively. Since $PV_{-} > PV_{+}$, the result is positive.
B is incorrect because reversing the numerator to $PV_{+} - PV_{-}$ produces a negative value, which contradicts the definition.
C is incorrect because it omits the division by 2. The average of the up and down price changes is used, not their total difference.