Right option is (c) 4
Easy explanation: The registers in which data can be shifted serially or parallelly are known as shift registers. Based on how binary information is entered or shifted out, shift registers are classified into 4 categories, viz., Serial-In/Serial-Out(SISO), Serial-In/Parallel-Out (SIPO), Parallel-In/Serial-Out (PISO), Parallel-In/Parallel-Out (PIPO).