Final answer:
The correct sentence to complete the summary is about how the invention of electricity and manufacturing increased the accessibility of ice cream. The option (C) is correct.
Step-by-step explanation:
The appropriate sentence to insert between the two bolded sentences to complete the summary is The demand for ice cream and the invention of electricity and manufacturing made ice cream more accessible.
This sentence directly ties to the preceding information about refrigeration making it easier to store and transport foods and the description of industrial advancements. It acknowledges how the invention of electricity and the growth in the manufacturing sector enabled easier access to ice cream, which is consistent with the context provided. Therefore, option (C) is correct.