Which of the following factors is unique for the development of the aircraft industry in California?

Step 1: Analyze the question The question asks for the factor that is unique (specific) to California's aircraft industry. Factors like labour, politics and government support are general to many industries anywhere, but a unique factor must relate to California's own physical environment.

Step 2: Explain the concept Aircraft manufacturing in Southern California (Los Angeles, San Diego, Burbank, Long Beach) grew because of several factors:

• Climate: Southern California has many sunny, clear days with little fog or rain, so test flights can go on almost all year.
• Open land: Flat, wide areas are ideal for airfields and large assembly plants.
• Capital and skilled labour: Available, but also found in other regions.
• Government contracts: Defence contracts, especially during World War II, were strong, not "limited".

Step 3: Evaluate the options

• A. Cheap labour: Aircraft production needs highly skilled, well-paid workers, and cheap labour is not specific to California. ✘
• B. Peaceful political atmosphere: This is a general condition for any industry. It is not unique to California. ✘
• C. Government limited support: This is wrong. The industry grew with heavy government support through defence contracts. ✘
• D. Clear sky which favours testing of aircraft: This depends on California's own climate, which gives clear skies and good visibility for test flights. ✔

Step 4: Answer The correct answer is D.

Exam tip: When you see the word "unique" or "peculiar" in an industrial location question, look for the option that ties to the physical environment of that place (climate, relief, resources) rather than general factors like labour, peace or capital.