Which of the following devices commonly utilize magnets?

Computer hard drives and microphones commonly utilize magnets due to their reliance on magnetic principles for data storage and sound recording.

In computer hard drives, data is stored on magnetic disks. The hard drive uses read/write heads that interact with the magnetic fields on the disk to encode and retrieve data. This technology enables efficient data storage and access, utilizing the inherent properties of magnets to maintain information.

Microphones also use magnets, particularly in dynamic microphones. In this type of microphone, sound waves cause a diaphragm to vibrate. This diaphragm is attached to a coil of wire positioned within a magnetic field created by a magnet. When the diaphragm moves, it induces an electrical current in the coil, converting sound waves into electrical signals that can be amplified or recorded.

By contrast, devices like remote controls and televisions rely more on electrical signals rather than magnetic mechanisms. Flashlights primarily work on batteries to produce light, while scissors and knives are tools that serve mechanical functions unrelated to magnetic forces. Therefore, the correct option emphasizes the essential use of magnets in the functioning of both computer hard drives and microphones, distinguishing it from the other choices.