Final answer:
It is appropriate to shift tenses in a sentence when the writer signals a change in time, to clearly delineate different time periods within a text. Consistency in verb tense is generally expected, but shifting tenses can be used to indicate when events have occurred.
Step-by-step explanation:
The question "When is it okay to shift tenses in a sentence?" refers to the rules of verb tense consistency that are important for clear and coherent writing. The correct answer is B, "When the writer signals a change in time." It is important to maintain tense consistency throughout a piece of writing, but sometimes, to indicate a difference in time, you need to change tenses. This change helps make clear to the reader when an action or event took place relative to others.
In literary present tense, for example, actions within a narrative or discussions of literary works are typically in the present tense. But when referring to actions that the characters have done in the past or events in the author's life that are not part of the story being discussed, past tense should be used. Overall, when a writer signals a change in time by transitioning from general discussion to specific past events, a shift in tense is appropriate and necessary for clarity.