A $10$ $kHz$ even-symmetric square wave is passed through a bandpass filter with centre frequency at $30$ $kHz$ and $3$ $dB$ passband of $6$ $kHz$. The filter output is
- a highly attenuated square wave at $10$ $kHz$.
- nearly zero.
- a nearly perfect cosine wave at $30$ $kHz$
- a nearly perfect sine wave at $30$ $kHz$.