Concept:Second generation computers are identified by the electronic component they used in place of vacuum tubes.
Explanation:First generation computers used vacuum tubes, which were bulky and consumed a lot of power.
Second generation computers used discrete transistors instead of vacuum tubes.
Transistors made computers smaller, faster, cheaper, and more reliable.
Integrated circuits were introduced in the third generation of computers.
Micro-chips became common in later generations, such as the fourth generation.
The presence of these components clearly separates each generation of computers.
Since the question asks for a characteristic feature of the second generation, the component is the transistor.
Answer:B. transistors