Answer:
the answer to the question is D
The answer is concrete.
<span>The Romans' ingenious use of concrete was
instrumental in the construction of the great cathedrals of Europe 1,000 years
later. Vaulting of concrete completed the building of the great cathedrals and amphitheater
of the Romans. It also made the Pantheon dome and the Palestrina’s Sanctuary of
Fortuna Primigenia. </span>
Primary source is the firsthand experience and evidence of an event, where the any given information first appeared (initial report). The secondary source uses the first source in order to give its information (for example: document that analyzes primary source documents).
When analyzing historical event a researcher use a secondary source instead of a primary source because he uses the primary source as the imput information (facts, events, dates, names) in order to analyze them, connect them and explain them in his work.
