The correct answer is: D. memory
A flip-flop is a memory element that stores a binary digit as a low or high voltage. It is a basic building block of digital circuits and is used in a variety of applications, such as counters, registers, and shift registers.
A chip is a small piece of semiconductor material that contains electronic circuits. It is used to build electronic devices, such as computers, cell phones, and televisions.
A bus is a data transmission line that allows multiple devices to share data. It is used in computers and other electronic devices.
I/O stands for input/output. It is the process of transferring data between a computer and an external device.
None of the above options are memory elements.