Which line most clearly shows the theme of a story marta gasped when she discovered the necklace was no longer around her neck or james resolved to make time for his friends rather than focusing on making money.

The theme of a story is not only is what the story may be about, but what the story or author teaches. "James resolved to make time for his friends rather than focusing on making money", would be a correct example of introducing a theme to a story.
"Marta gasped when she discovered the necklace was no longer around her neck" would introduce the plot, or what is going to happen, in the story.