Explanation : Possible strings of length 4 are: 0001, 0111, 0011, 0101, 0123, 2323, 2333, 2223, 2233, 2301. Total 10 strings are possible. So, option (C) is correct.
Explanation : In option (B), Multiplication operation is replaced with Shift Operator . It reduce the operator strength because shift operator is less expensive than multiplication operation. So option (B) is correct.