In L1, we can compare a number of a's with a number of b's and L2 we can compare a number of b's with the number of c's by a stack, so both are CFL and we know that CFL is closed under union operation, So L3 is also CFL.

Hence, L1, L2 and L3 are CFL...

Hence, L1, L2 and L3 are CFL...