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1 question at a time
but its just to check them? i just need to know if any are wrong
I think some are wrong, viz:
3. The US cannot regulate the manufacture of cars not manufactured on US soil, so a better answer may be the amelioration of air pollution. Regulation of cars falls into three categories: safety, pollution control, and fuel economy, which is sort of indirect pollution control or just political feel-good BS. So there is definitely a fair amount of regulation that is designed to control pollution.
7. I think the better answer is that if goods are used together (peanut butter and jelly, soap and bath towels) then an increase in demand for one will increase the demand for the other. Your answer suggests that if the demand for peanut butter goes up, the demand for jelly will go DOWN, which doesn't seem likely. You are correct for goods that are substitute goods, like skiing vacations and beach vacations. If the demand for ski trips goes up, we can expect the demand for beach vacation trips to go down, because the goods substitute or each other -- you can use one or the other, but not both. But that's not goods bought together, those are goods that are used together.
8. I think a better answer is that demand for a good can be inelastic at a LOW price and elastic at a high price. Remember, elasticicity means sensitivity to price. People are more insensitive to price when it's lower. If the cost of gasoline were 10 cents per gallon, practically nobody would change his driving behaviuor if it doubled, to 20 cents per gallon. So at that price, the demand is inelastic -- not sensitive to price. But when gas costs $4 a gallon, people will probably radically change their driving habits if it doubles, to $8 a gallon. At that price range, demand for gasoline is elastic -- people are sensitive to the price.