Introduction:
The 74HC195 is a 4-bit parallel access shift register, which means it can store and shift data in parallel format. It has four parallel input lines (D0-D3), four parallel output lines (Q0-Q3), and four control signals (S0-S3). It can be used for various operations depending on how the control signals are configured.

Explanation:
The correct answer is option D, which states that the 74HC195 can be used for all of the mentioned operations. Let's understand each operation in detail:

a) Serial in/serial out operation:
In this operation, the data is serially shifted into the shift register one bit at a time, and then it is serially shifted out one bit at a time. The control signals S0 and S3 are used to control the shift operation. S0 is used to load data into the shift register, and S3 is used to shift the data out. The parallel output lines Q0-Q3 can be used to read the shifted out data.

b) Serial in/parallel out operation:
In this operation, the data is serially shifted into the shift register one bit at a time, but it is parallelly read out from the parallel output lines. The control signals S0 and S3 are used in a similar way as in the serial in/serial out operation.

c) Parallel in/serial out operation:
In this operation, the data is parallelly loaded into the shift register through the parallel input lines, and then it is serially shifted out one bit at a time. The control signals S0 and S3 are used to control the shift operation. The parallel input lines D0-D3 can be used to load the data, and the shifted out data can be read from the parallel output lines Q0-Q3.

d) All of the mentioned:
As explained above, the 74HC195 can be used for all of the mentioned operations. It provides flexibility in terms of data input/output formats, allowing various applications to be implemented using this shift register.

Conclusion:
The 74HC195 4-bit parallel access shift register can be used for serial in/serial out, serial in/parallel out, and parallel in/serial out operations. It provides versatility in data handling and can be utilized in a wide range of applications.