Which of the following was a social cost associated with the development of the internal combustion engine used in most cars?

A. People were able to use their horses for new tasks.

B. New jobs were created.

C. Blacksmiths needed to gain new skills to continue working.

D. Families were able to travel farther more easily.

I believe the answer to your question would be C. Mainly because of the development of this engine Blacksmiths would have to learn news things in order to keep their career as a Blacksmith itself.

C. Blacksmiths needed to gain new skills to continue working.

Explanation:

Nikolaus August Otto was the engineer who invented and built the first four-stroke internal combustion engine and determined the theoretical cycle under which the explosion engine, the well-known Otto cycle, works.

The engine invented by Otto demonstrated numerous advantages over the steam engine used at the time. One of them is the low weight, since steam engines needed huge reservoirs of water, besides fuel to be burned to heat the water, being in these cases charcoal or firewood. In addition to the low weight, the internal combustion engine had low fuel consumption, even this being benzene. Another factor was the power of Otto cycle internal combustion engines which also surpassed in size ratio with the steam engine.

Because of these advantages, the automotive industries received the pressure to produce cars that used this type of system. This forced blacksmiths to acquire new skills that would allow them to work with this new technology.