An article headline claimed that "drugs cause homelessness" due to a positive relationship found between homeless populations and drug use. educated psychologists thought this might be flawed, because they thought unemployment was influencing both drug use and homelessness. this is an example of:

The answer is a third variable.

A third variable or a confounding variable is a variable that influences two separate variables that are being measured. In this case the two separate variables being measured are drug use and homeless populations, the third variable here would be unemployment.

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.