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Answer:
Due to structure of engine.
Explanation:
Cars and trucks today powered by petroleum products because of their engine which only works when the petroleum products are used. When the petroleum products are burn in the engine, it produces small blasts which moves the piston and as a result the wheels of the car also start movement. Petroleum products are economically cheap due to its higher availability on the earth, easily available to the people, can be easily transported are the factors that make us use of petroleum products.
Answer:
they have lower levels of the neurotransmitter serotonin