Final answer:
In the 1950s, a large commercial aircraft was typically flown by a crew of five people, including the pilot, co-pilot, navigator, flight engineer, and radio operator.
Step-by-step explanation:
The question relates to the history of aviation, specifically the crew size needed to safely fly a large commercial aircraft in the 1950s. In that era, the crew required was typically a flight engineer, a radio operator, in addition to the pilot, co-pilot, and a navigator. So, the answer to the question is (a) 5 people. These roles were critical because the technology was not as advanced as today, requiring more human input for tasks such as navigation, engine monitoring, and communication with ground services.