Is the belief that nature is all that exists and that nothing supernatural exists?

This type of belief is called Naturalism. It is a philosophical belief in realism/reality, that only what we can physically see and explain is real and true. A modern view point would be that if something cannot be proved scientifically then it does not exist and that is naturalism.

the correct answer is modern american cars are not available due to trade restrictions.

trade between cuba and the united states have serious restrictions. the u.s. imposed an economic embargo on cuba, that among other things means that modern american cars are not available due to trade restrictions.

in response to some governmental actions of the authorities from cuba, president john f. kennedy proclaimed an embargo on trade between both countries in february 1962. the trade embargo remains active until this day and was implemented directly by the departments of commerce and the department of treasury.

in president trump’s administration, there is a national security presidential memorandum that "strengthens the policy of the u. s.", affecting trade with cuba.