Which of the following electronic technologies is the key technology for making the fourth-generation electronic computer?

The fourth generation of computers is built around the microprocessor, a whole CPU on a single chip.

Transistor-based machines mark the second generation, replacing bulky valves.

Integrated circuits define the third generation, packing many transistors onto one chip.

Vacuum-tube technology belongs to the first generation of computers.

The microprocessor let computing shrink to desktops and later to handheld devices.

Intel's 4004 in 1971 was the first commercial microprocessor.