The transfer function for a practical differentiator is modified from the ideal case to include frequency compensation for stability. The correct answer is (a) Vo(s)/V1(s) = -S*RF*C1/(1+R1*C1)^2. This transfer function represents the practical differentiator where the frequency response includes the effect of both the feedback resistor RF and capacitor C1, as well as the input-limiting resistor R1. The denominator term (1+R1*C1)^2 provides the frequency-dependent compensation for practical op-amp differentiators.