The correct answer is A. one.
A SISD (single data stream, single data stream) architecture is a type of computer architecture that has a single processor and a single data stream. The processor executes instructions one at a time, and the data stream is a sequence of data that is processed by the processor.
A control unit is a part of a computer that controls the execution of instructions. It fetches instructions from memory, decodes them, and then executes them. In a SISD architecture, there is only one control unit. It controls the execution of all instructions in the computer.
The other options are incorrect because they do not accurately reflect the number of control units in a SISD architecture. Option B is incorrect because it states that there are two control units in a SISD architecture. Option C is incorrect because it states that there are more than one control unit in a SISD architecture. Option D is incorrect because it states that there is no control unit in a SISD architecture. Option E is incorrect because it states that none of the above options are correct.