Given the channel features or objectives below. For each part, tell which line code(s) is (are) the best choice(s).

(a) The channel frequency response has a null at f = 0 hertz.
(b) The channel has a pass band from 0 to 10 kHz and it is desired to transmit data through it at 10,000 bits/s.
(c) At least one zero crossing per bit is desired for synchronization purposes.
(d) Built-in redundancy is desired for error-checking purposes.
(e) For simplicity of detection, distinct positive pulses are desired for ones and distinct negative pulses are desired for zeros.
(f) A discrete spectral line at the bit rate is desired from which to derive a clock at the bit rate.