When Eckels returns to the present, he is

(B) nervous of the slight change he can sense.

Explanation:

  the conflict is the challenge the main character need to solve to achieve their goals, is the major literary element because creates challenges in the story by addin uncertainty to if the goal would be achieved. in the story could be more than a single conflict, in fact, most of the stories have a diversity of them. the resolution creates a closure that may or may not be the end of the story.

  the basic types of conflict have been classified as "person againsta nature", "person against person" and "persona against self". nevertheless the basic types, some authors think that it could be more than only three types, for instance:

  i´m gonna give you a little summary about the three basic types that i think are the one importants for the question

  the confict involves stories where characters are against each other, is an external conflict, as in a gun fight or a robbery or it could be more subtle between the desires of the characters as in a love story. this type of conflict is very common in traditional literature, fairy tales and myths.

  is an external conflict between the character and an animal or a force of nature, like a tornado,a storm or even a rain. a great example of this is ernest hemingway´s "the old man and the sea"   in which the main character struggle with a marlin when he was fishing.

  in this case the conflict is internal, the character must overcome her or his own nature or make a choice between two paths.

  i hope the answer is correct and you. regards