A clocked array of circuits that passes data in steps along the array✓Bonne réponse
An array of operational amplifiers used for tri-state arithmetic operations
A digital mixer
An analog mixer
Explication
A shift register is a chain of clocked storage stages in which every clock pulse moves the stored data one position along the chain, which is what makes it useful for serial-to-parallel conversion and delay. The other choices describe amplifiers and mixers, which do not store data.