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

1. a highly attenuated square wave at $10$ $kHz$.
2. nearly zero.
3. a nearly perfect cosine wave at $30$ $kHz$
4. a nearly perfect sine wave at $30$ $kHz$.

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