Option B
Maximum data rate to transmit binary signal is 2H.Nyquist's Theorem - If the signal has V discrete levels over a transmission medium of bandwidth H, the maximum data rate = 2H log2 V bits/sec.
where H is the bandwidth, V is the discrete levels. Here H is 3 kHz and V is 2.
So, data rate = 2*3000 log22 bps = 6000 bps.