Answer:
(b) transistors
Step-by-step explanation:
You want to know the technology improvement that drastically reduced the size of early computers.
Transistors
The logic of early computers was implemented using relays, and/or vacuum tubes. Both of these technologies required several cubic inches and perhaps several watts per logic element.
With the advent of the transistor, both size and power could be reduced by several orders of magnitude. Transistors allowed computers to be made smaller, faster, more powerful, and more reliable.
Transistorized computers occupied substantially less space than vacuum tube computers. In general, the space allocated for storage devices (magnetic disk drives and tape drives) became a larger fraction of the total space required for a computer installation.