Which of the following sentences contains a dangling modifier?

A dangling modifier occurs when the subject of the modifier is not clearly stated in the sentence, leading to confusion about what the modifier is referring to. In this case, the sentence "Always getting into trouble, her life changes" contains a dangling modifier. The phrase "always getting into trouble" is meant to modify a subject, but the noun "her life" does not make sense in this context, as it is not "her life" that gets into trouble. This creates ambiguity about who is actually getting into trouble.

In contrast, the other sentences clearly link the actions in the modifying phrases to a suitable subject. For example, in "Running all day, she felt exhausted," it is clear that "she" is the one who is running and thus feeling exhausted. Similarly, "Eating dinner, he watched a movie" clearly indicates that "he" is both eating dinner and watching a movie. In "Studying for hours, he mastered the subject," it is evident that "he" is the one studying and mastering the subject. Therefore, only the sentence with the dangling modifier lacks clarity and proper relational structure between the modifier and the subject.