Question

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 enemys 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 readers understanding of which technological advances were used during fieldwork
by changing the readers perceptions about how fieldwork could help 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

Explanation:

The central idea is about Civil War spying involving fieldwork. To develop this, more details about who did fieldwork (agents) and how (methods like observation, infiltration) would show its prevalence. The first option focuses on tech (not fieldwork's role). The second changes perception about Union cause (not fieldwork itself). The fourth adds moral issues (not directly developing fieldwork as main means). Only the third, by giving details of who (spies) and how (field - work methods), develops the central idea.

Answer:

by including more detailed information about who did fieldwork for the Union and how it was done