Read this excerpt from the dark game.
another thing that changed very little in the years between the wars was the means of obtaining military intelligence. although the use of photography and the telegraph brought some technological advances, the craft of spying on the enemy's army still relied on fieldwork.
in the rest of the text, how does the author develop this central idea that spying during the civil war still involved mostly fieldwork?
by enhancing the reader’s understanding of which technological advances were used during fieldwork
by changing the reader’s perceptions about how fieldwork could the union cause
by including more detailed information about who did fieldwork for the union and how it was done
by adding complexity to the topic by raising the moral issues involved in fieldwork and other espionage

The third alternative is correct (C).

Between one war and another, one can expect technology to make a difference, whether in armament production or tactics. Thus, between one war and another, armaments became more sophisticated and strategies more elaborate.

However, in the first half of the twentieth century, when the two wars happened, espionage technology had not developed. The two world wars took place during this period, that is, in scientifically short spacing. For the espionage services, this short period did not allow great advances, only the photos and the telegraph.

In this context, fieldwork for espionage was still essential. The narrator then seeks to better detail the functioning of this mechanism, pointing out those responsible for the practice and how it was performed.

a.) it provides a clue to solve the mystery.

it means that the hockey puck was traveling very fast.