Final answer:
The line from Mark Twain's 'The Adventures of Tom Sawyer' suggesting a happy resolution is 'With a grin, Tom realized that everything was finally falling into place,' as it implies positive outcomes.
Step-by-step explanation:
In Mark Twain's novel The Adventures of Tom Sawyer, the line that most likely indicates a happy resolution developing in the story is: c) With a grin, Tom realized that everything was finally falling into place. This line suggests a sense of relief and satisfaction, which is often associated with positive outcomes and resolutions in storytelling. In contrast, the other options all include negative language that implies conflict or challenges, such as "storm clouds," "heart sank," and "sense of doom," which are not indicative of a happy resolution.