Which frequency demodulator circuit satisfies the stated configurational conditions ?

Which frequency demodulator circuit satisfies the stated configurational conditions ?
A. Diode (D2) in reversed biased connection.
B. Inclusion of a large value capacitor (C5) in the circuit.
C. Output is taken somewhere else.
d. Frequency Demodulation is the salient operational characteristic.

a. Zero Crossing Detector
b. Foster-Seeley Discriminator
c. Ratio Detector
d. Both (B & C)

Correct Answer : c. Ratio Detector

Explanation :

Ratio detector varies from Foster-Seeley discriminator by all four statements in the question,while ZCD operates on the principle of instantaneous frequency and the time difference between adjacent zero cross-over points. Therefore, options a,b & d are absolutely not feasible since ratio detector is only frequency demodulator circuit that fulfill these conditions. In fact, all mentioned conditions are the distinguishable features of ratio detector in comparison to other detectors.