The correct answer is (d).
A buffer is a temporary storage area that compensates for differences in data rate and data flow between devices. It is used to store data that is being transferred from one device to another, and to smooth out any fluctuations in the data flow. This can be important in situations where the data rate of the two devices is not the same, or where there is a lot of latency in the connection between the devices.
A bus is a physical connection between devices that allows them to communicate with each other. It is a shared resource, and all devices on the bus must share the same bandwidth. This can lead to problems if there are too many devices on the bus, or if the devices are not communicating at the same speed.
A channel is a logical connection between devices. It is a dedicated path for data to flow between two devices, and it does not share the same bandwidth as other channels. This makes it a more reliable way to transfer data, and it is often used for applications that require high-speed data transfer.
A modem is a device that converts digital data into analog signals, and vice versa. It is used to connect computers to the internet, and it is also used for other applications such as faxing and voice over IP.
In conclusion, the correct answer is (d). A buffer is a temporary storage area that compensates for differences in data rate and data flow between devices.