Demand is a powerful force in a free market. in three to four sentences, explain some of the factors that cause changes in demand and why it is important for consumers to understand these changes.

The Factors that affect the demand are First, Willingness to buy convey a desire, based on what economists call tastes and preferences.  You may need nor want something, you will not buy it then the Ability to buy convey that income is important. Second, size or composition of the population can affect demand. The more children a family has, the greater their demand for clothing. There is a need for the Consumer to understand the changes because if there is greater demand there is a greater supply. 

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.

new communications technology has affected the way social movements are organized because nowadays, social movements rely on social networks and the media to get different people with a similar way of thinking in contact, and thus, get them to mobilize for a greater cause.

individuals only participate in collective action when they feel identified with it. is in this aspect that social media becomes relevant, because it guarantees communication among all individuals and organizes the social actions that are going to be carried out, i.e., the social movements.

in addition, being covered by the media is important to validate the message and make it relevant in the social agenda, as well as to reach more people who can share interests, appealing to public sympathy for their cause.

in conclusion, it is by social networks and social media that social movement is given birth; by connecting different individuals with similar ideas and organizing them to mobilize for a greater cause.