Final answer:
Decreasing petrol prices is likely to lead to an increase in demand for automobiles as the overall cost of driving is reduced, making car ownership and operation more economical for consumers.
Step-by-step explanation:
When petrol prices decrease and are widely expected to stay low, this generally leads to an increase in demand for automobiles, as driving becomes more economical for consumers. The lesser expense on fuel can make owning and operating a vehicle cheaper, potentially making it an attractive option for more people. This scenario leverages the basic economic principle that ceteris paribus (all other factors being equal), a decrease in the cost of a complementary good — in this case, petrol for cars — will increase the demand for the related good.
Therefore, we would expect an a) Increase in demand for automobiles. Lower fuel costs reduce the overall cost of driving, which can make consumers more likely to purchase vehicles, particularly those that are less fuel-efficient and might have previously been more costly to run. Conversely, when petrol prices are high, consumers may be discouraged from buying automobiles due to the higher running costs or might prefer more fuel-efficient or alternative fuel vehicles.