Concept:The technology that powered first-generation computers was the vacuum tube, which served as the main electronic switching component.
Explanation:First-generation computers were developed during the late 1940s and the early 1950s.
They used vacuum tubes to perform calculations and to store data in memory.
Vacuum tubes controlled electric current by amplifying and switching electronic signals.
These tubes were large, generated enormous amounts of heat, consumed a lot of power, and broke down frequently.
Consequently, first-generation computers were enormous in size, costly to run, and not very reliable.
Second-generation computers replaced vacuum tubes with transistors, making machines smaller, faster, and more dependable.
Integrated circuits came next in the third generation, followed by microprocessors in later generations.
These newer technologies brought compact, powerful computers, but the very first computers depended on vacuum tubes.
Answer:D. vacuum tubes.