Question

the main, or central, idea of the passage is participants in the underground railroad used code words in order to protect formerly enslaved people and those helping them. how does the detail in bold develop the main idea?

in the decades before the civil war, thousands of enslaved americans fled captivity via the underground railroad, a secret network of escape routes. volunteers provided navigation, provisions, and hiding places for the fugitives—highly dangerous work for all involved. those who were fleeing slavery could be captured and returned to bondage, while those who helped them could be jailed. the organizers reduced the risk by using code words to communicate sensitive information. for example, guides were referred to as \conductors,\ safe houses were called \stations,\ and the people who hid the formerly enslaved were \stationmasters.\ the formerly enslaved people themselves were referred to as \cargo,\ \packages,\ or \goods\ in order to preserve their safety.
consider this text from a letter sent between two volunteers: \i suppose you are somewhat uneasy because the goods did not come safe to hand on monday evening . . . the train only was from harrisburg to reading, and as it happened, the goods had to stay all night with us.\

it details the various barriers along the path to the northern states,

it gives a reason why the volunteers took such significant risks.

it emphasizes the risk faced by those involved with the underground railroad.

Explanation:

The bolded text describes the severe dangers (captured return to bondage for the enslaved, jail for helpers) that Underground Railroad participants faced. This establishes the urgent need for the code words mentioned in the main idea, by highlighting the high stakes that made secret communication necessary.

Answer:

It emphasizes the risk faced by those involved with the Underground Railroad.