The correct answer is option 'D' - ULSI (Ultra Large Scale Integration).

Fifth generation computers were developed in the 1980s and were characterized by their use of ULSI technology. ULSI refers to the integration of a very large number of transistors and other electronic components onto a single chip. This allowed for significant advancements in computing power and efficiency.

Here is a detailed explanation of the electronic components used in fifth generation computers:

1. Transistors:
- Transistors are electronic devices that can amplify or switch electronic signals and electrical power.
- They were the basic building blocks of early computers and were used for logic gates, amplifiers, and switching circuits.
- Transistors were first used in the second generation of computers and played a key role in the development of subsequent generations.

2. Integrated Circuits:
- Integrated circuits (ICs) are small electronic circuits that are fabricated onto a single semiconductor material, usually silicon.
- ICs consist of multiple electronic components such as transistors, resistors, capacitors, and diodes, all interconnected on a single chip.
- They were introduced in the third generation of computers and greatly increased computing power and reduced the size of electronic devices.

3. VLSI (Very Large Scale Integration):
- VLSI refers to the integration of a large number of transistors and other electronic components onto a single chip.
- It allowed for the creation of more complex and powerful circuits.
- VLSI technology was used in the fourth generation of computers and paved the way for the development of microprocessors.

4. ULSI (Ultra Large Scale Integration):
- ULSI is an extension of VLSI technology that allows for an even greater number of transistors and electronic components to be integrated onto a single chip.
- ULSI technology was used in the fifth generation of computers.
- It enabled the development of highly advanced microprocessors, capable of processing vast amounts of data and performing complex tasks.

In summary, while transistors and integrated circuits were used in earlier generations of computers, it was the introduction of VLSI and ULSI technology in the fourth and fifth generations that brought about significant advancements in computing power and efficiency. ULSI, in particular, allowed for the integration of an extremely large number of electronic components onto a single chip, leading to the development of highly advanced microprocessors.