What audio shaping network is added at an FM receiver to restore proportionally attenuated lower audio frequencies?

In FM communications, higher audio frequencies are often artificially boosted at the transmitter to improve the signal-to-noise ratio, a process called 'pre-emphasis'. To restore the original, natural audio balance at the receiving end, a complementary circuit called a 'de-emphasis network' is required. The de-emphasis network rolls off or attenuates those artificially boosted higher audio frequencies. By doing so, it effectively restores the proportionally attenuated lower audio frequencies back to their correct relative levels. Selecting 'pre-emphasis network' is incorrect because that process must occur at the transmitter before the signal is sent, not at the receiver. The other options are fabricated distractors that do not perform audio equalization.