Let us see the statements one by one :
Statement 1 is false since it uses only sequential circuits and no need of additional circuitry as in microprogrammed control unit
Statement 2 is false since the statement is true for hardwired control unit.In microprogrammed control unit changes can be reflected by doing the changes in control word of the control memory.
Statement 3 is false as well since in vertical microprogrammed unit we use encoded form of control signal since say we have 128 control signals then we use 7 bits to represent one of the 128 control signals.
Statement 4 is false as well since in terms of flexibility , vertical microprogramming is the best since in case of modification say we have 128 control signals , in worst case , in case of horizontal microprogramming all the 128 bits of the control word concerned may need to be modified.But in case of vertical microprogramming we need to modify only 7 bits here to do that modifcation.
Hence A) is the correct option.
