What is the name of a circuit that generates a signal at a specific frequency?

An oscillator is a fundamental electronic circuit that generates a continuous, alternating waveform at a specific, steady frequency. In amateur radio, oscillators provide the raw carrier wave for transmitters and the local tuning frequencies for receivers. The other choices do not generate raw frequencies. Modulators alter an already existing signal to imprint information onto it, such as voice or data. A low-pass filter merely allows lower frequencies to pass through while blocking higher ones.