To answer this question, it is important to understand the different types of storage devices and their connections to the CPU box.

Storage devices are used to store data and can be classified into two main categories: primary storage devices and secondary storage devices. Primary storage devices include random-access memory (RAM) and cache memory, while secondary storage devices include devices like CDs, magnetic tapes, microphones, and flash drives.

Primary storage devices are directly connected to the CPU through the motherboard, and they hold the data that the CPU is currently using or processing. Secondary storage devices, on the other hand, are used for long-term storage of data and are not directly connected to the CPU.

Among the options provided, the correct answer is a flash drive. Let's understand why:

- a) CD: CDs are a type of secondary storage device that can store data, but they are not connected to a port on the CPU box. Instead, they are inserted into a CD-ROM drive or DVD drive, which is connected to the CPU box through a separate cable or port.

- b) Magnetic tape: Magnetic tapes are another type of secondary storage device, commonly used for backup or archival purposes. Like CDs, they are not directly connected to a port on the CPU box. Instead, they are connected to a tape drive, which is then connected to the CPU box.

- c) Microphone: A microphone is an input device that is used to capture audio. It does not store data and therefore does not need to be connected to a port on the CPU box. Instead, it is connected to a separate input port, such as a microphone jack, on the CPU box or the sound card.

- d) Flash drive: A flash drive, also known as a USB flash drive or a thumb drive, is a type of secondary storage device that can store data. It needs to be connected to a port on the CPU box, typically a USB port. This connection allows the CPU to read from and write to the flash drive.

In summary, among the given options, only a flash drive needs to be connected to a port present on the CPU box. CDs, magnetic tapes, and microphones have their own dedicated connections or ports separate from the CPU box.