Answer:
The best example of a rhetorical device from the given options is C) Repetition
Repetition is a commonly used rhetorical device where a word, phrase, or idea is repeated multiple times for emphasis and to create a lasting impression on the audience. This technique can be used to emphasize a point, create a rhythm or pattern, or reinforce a theme.
Subject-actecedent agreement is a grammatical rule that ensures that the subject of a sentence agrees with the verb in number and person. While important for clear communication, it is not a rhetorical device.
Tragedy is a type of drama characterized by a serious and somber tone, often involving a protagonist who suffers a downfall or catastrophe. While it can be a powerful literary genre, it is not a rhetorical device.
Cause-effect is a logical relationship between events or actions where one event (the cause) leads to another event (the effect). While it is an important concept in critical thinking and analysis, it is not a rhetorical device.