Part-A: how the errors are introduced in quantum key distribution.

Part-B:Explain how the intrusion is detected in BB84 QKD protocol.

Part-C: Explain the impact of changing the encoding scheme of BB84 QKD protocol such that both of the states of each basis have same bits encoded; for example: |e1> = 0, |e2> = 0, |f1> = 1, |f2> = 1 Would it be possible to extract the final shared bits after this encoding? If not, then can you suggest any changes in the protocol so that it will work.