Final answer:
The underlined portion of the sentence does not contain a mistake, and the best alternative is option D, "which was a relief to everyone involved in the tragedy," as it correctly conveys the intended meaning and is grammatically accurate.
Step-by-step explanation:
The question asks to identify if there is a mistake in the underlined portion of the sentence and to choose the best option among the given alternatives.
The original sentence is, "The attorney planned to settle the case out of court, which, to everyone involved in the tragedy, was a relief." The alternatives provided offer different ways to express the idea that settling the case out of court was a relief to those involved.
Upon evaluation, it's clear that option D, "which was a relief to everyone involved in the tragedy," preserves the meaning of the original sentence most effectively and is grammatically correct. Therefore, the final answer is option D, as this option does not require any improvement or correction.