Which of the following languages are regular. Prove (by providing a regular expression) or disprove.

a. L1 = {aⁱ b^j c^k d^l | (i + j)mod 2 = (k + l)mod 2 , i, j, k, l 0}

b. L2 = {aⁱ b^j c^k d^l | (i + j) = (k + l), i, j, k, l 0}

c. L3 = {wxw^R | w {a, b} , x {c}} ( w^R is reverse of string w).