Answer: C
Correct answer: Hard disk drive
A hard disk drive holds far more than any of the others - terabytes, where the optical and magnetic media listed hold gigabytes or megabytes. The capacities are worth knowing in order, since the comparison is a standard question. A floppy disk held 1.44 MB. A CD holds about 700 MB. A DVD holds 4.7 GB single-layer and 8.5 GB dual-layer. A Blu-ray disc holds 25 GB per layer. A hard disk today holds several terabytes. The optical discs differ chiefly in the wavelength of the laser used: a shorter wavelength focuses to a smaller spot, so more pits fit on the same surface. CD uses infrared at 780 nm, DVD red at 650 nm, and Blu-ray blue-violet at 405 nm - which is where its name comes from. Solid-state drives now rival hard disks in capacity while being far faster, and cloud storage is effectively unlimited but depends on a connection.