on A 12-Bit result register value has to be casted for a 16-Bit data address. Which is the first instruction step Select one: O a. Fill out the 4 highest significant Bits with value 0 O b. Fill out the 4 lowest significant Bits with value 1 OC. Fill out the 4 highest significant Bits with value 1 O d. Fill out the 4 lowest significant Bits with value O