Which part of Source B or Source C helps you best visualize what it was like for the civilians who were exposed to the atomic bomb?

Hello. You have not shown the sources to which this question refers, which makes it impossible for the question to be answered accurately. However, I will try to help you in the best possible way.

A source that helps you to visualize a moment well, is one that presents a highly descriptive language that presents a large number of adjectives that inform you of many characteristics of that event, thus allowing you to form a mental image of what happened. Therefore, you should look for this type of language in your sources to find out which is the most efficient.

pretty sure a is right