Consider a Feistel cipher with four rounds. Then the plaintext is denoted as $P=(L_0,R_0)$

and the corresponding ciphertext is $C=(L_4,R_4).$ What is the simplest form of the ciphertext

$C,$ in terms of $L_0,R_0,$ and the subkeys, for each of the following round functions? $($You

should clearly show steps about how you get the answer$)$

A$)F(R_{i-1},K_i)=0$

B$)F(R_{i-1},K_i)=R_{i-1}$

C$)F(R_{i-1},K_i)=R_{i-1}o+K_i$