(d) [3 marks] Now suppose that the BCD checker circuit is to be modied to be used as a module in a larger n-bit BCD checker design capable of checking if the input of an n-bit number is a valid BCD code, where n is a multiple of 4. Modify the circuit in part (c) using additional logic gates to yield a new module that has an additional input BCDin as shown in the gure below such that the output BCDout is 1 if and only if the 4-bit input A3A2A1A0 is a valid BCD code AND the input BCDin is 1. Show how several of these new modules could be used to check the validity of an 8-bit BCD code X7X6X5X4X3X2X1X0.