When researchers cannot randomly assign participants and manipulate conditions in the real world, they can sometimes compromise by conducting experiments

The answer is natural experiments.

Explanation:

In natural experiments, the groups of participants are not controlled by the researchers. They are often done when lab experiments would interfere with the validity of the study, or when applying it would be unethical (for example, experiments related to diseases are often studied in a natural environment).

Natural experiments are recorded through observation. They usually seek to understand the effects of an environmental factor in a sample population.

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.

the template that is used is page layout then the margins option and finally choose the normal option.